Ignition Coil Selection.

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I have a friend who has a 1973 ford ranchero, the previous owner of the ranchero had a 1976 ford 460 engine installed in it. The engine has what i believe to be a 1973 ford 429 distributor installed in it. The distributor has only a single vacuum advance diaphram (not a dual vacuum advance/retard diaphram) installed on it.
Recently he had a mallory unilite 502 breakerless electronic conversion kit installed inside of the distributor, so there are no more contact points installed in it. He is still using the 1973 original equipment type of ignition coil. The spark plug gap for the 1976 ford 460 engine is specified to be 0.042" to 0.046" in the ford repair manuals. The spark plug gap for the 1973 ford 429 engine is specified to be 0.032"to 0.036" in the ford repair manuals.

He currently has his spark plugs gapped at 0.042" to 0.046", but someone had told him that the 0.042" to 0.046" spark plug gap might be too large for the 1973 ignition coil and the coil might get alot warmer/hotter than if the spark plug gap was set from 0.042" to 0.046", is this true?

The ford motor company had switched to a different ignition coil in 1974 when they had switched from contact points to electronic ignitions on many of their cars and trucks. This new 1974 ignition coil had slightly less resistance and a slightly higher inductance rate than the 1973 and earlier/older ignition coils. The 1974 and newer coils probably have a slightly higher voltage output also.

He was told by someone that the 1976 original equipment ford motorcraft four barrel carburetor that he has on his engine, was designed to run a little bit leaner (with all of the newer emissions equipment that was being installed on these engines at the ford factories at that time) than the 1973 and earlier ford carburetors. So it would be better if he had gapped his spark plugs from 0.042" to 0.046" instead of 0.032" to 0.036" like the 1973 and earlier engines. 

So here are my questions: Should he switch to a 1974-newer style coil? Or should he switch to a higher voltage coil with a higher inductance rate and less resistance? 
Someone had recommended an Accel 8140 coil to him. This accel coil has 42,000 volts maximum output and it has less resistance and more inductance than the original 1973 ford type coil. I will post the specifications for this coil below. 
Primary Resistance: 1.400 ohms
Maximum Voltage: 42,000 V
Turns Ratio: 94:1
Secondary Resistance: 9.2K ohms.
Another person had recommended a mallory 29219 coil, I will post the specifications for this coil below.
Primary Resistance: 1.400 ohms
Maximum Voltage: 58,000 V
Turns Ratio: 112:1
Secondary Resistance: 10.00K ohms
Inductance: 6.6 mH
Peak Current: 180 mA
Spark Duration: 300 uS
A third person had recommended a mallory 29216 coil, I will post the specifications for this coil below.
Primary Resistance: 0.700 ohms
Maximum Voltage: 51,000 V
Turns Ratio: 99:1
Secondary Resistance: 8.9K ohms
Inductance: 6.6 mH
Peak Current: 180 mA
Spark Duration: 400 uS
There was also someone who had recommended an original equipment type replacement coil. I will post the specifications for the 1973 original equipment replacement ford coil below.
Inductance (mH): 6.6
Minimum Primary Resistance Range: 1.50 Ohms
Minimum Secondary Resistance Range: 11,000 Ohms.
I was told that the maximum output voltage of these factory original equipment type coils is about 20,000 volts. Is this true? Is more voltage really necessary?

Next I will post the specifications for another 1973 original equipment replacement ford coil below. This next coil is from the same company as the coil listed above, but it is a better quality and it costs a few dollars more.
Inductance (mH): 6.6
Minimum Primary Resistance Range: 1.50 Ohms
Minimum Secondary Resistance Range: 10,000 Ohms

Next I will post the specifications for a 1974 through 1978 original equipment replacement ford coil below. 
Inductance (mH): 6.2
Minimum Primary Resistance Range: 1.3 Ohms
Minimum Secondary Resistance Range: 9,000 Ohms

I was told that the maximum output voltage for these original equipment 1974-1978 replacement coils is about 20,000 to 23,000 volts. Is this true? Is more voltage really necessary? If it is necessary, how is it necessary?
Next I will post the specifications for another 1974 through 1978 original equipment replacement ford coil below. This next coil is from the same company as the coil listed above, but it is a better quality and it costs a few dollars more.

Inductance (mH): 7.6
Minimum Primary Resistance Range: 1.3 Ohms
Minimum Secondary Resistance Range: 8,000 - 10,000 Ohms

My friend only uses this car as a daily driver sometimes and he does not use this car for any type of racing or high performance driving. Sometimes he has to rev his engine up to 3400 to 4000 RPM's when he is entering a onto a highway, but that is the only time that he revs the engine that high. So will a higher voltage/lower resistance/higher induction coil really be necessary? 

Also, what do you think that he should set/adjust his spark plug gaps to?

I can tell you more about his engine so it will be easier for you to give answers to me: His engine has an original equipment type (stock) camshaft installed in it. His engine does not have any high performance/racing parts installed on it, he had mentioned that he is probably going to keep it that way.

He sometimes has to park his car in a large warehouse-garage where their are other people working, so he needs good/low exhaust emissions out of his exhaust tailpipe.

Also, If any of you know of anyone who has greatly increased the Size and CFM's of their carburetors (for extra fuel intake), due to the fact that they were adding on other high performance parts to their engine and they still have good/low exhaust emissions out of their exhaust tailpipe, (possibly due to the fact that they had added a higher voltage/lower resistance/higher inductance ignition coil), I would really like to hear your stories.

Thank you for any answers that you can give to us.

Edited by dave302 - 23-November-2014 at 9:39AM