1971 Torino driveshaft length

IIRC i've seen shaft length info in factory manuals ... ?

FWIW i don't trust and rightfully so the flange to output shaft or flange to seal measuring method.

i'm still smoked over my brand new never been used too short drive shaft they built me using their  method. $250+ and too short for me to sleep at night. a little over 1/2 yoke engagement on the output shaft. intended for a C6 it's even shorter when i swapped to the Toploader

for the most accurate measurement, set the slip yoke as far in as it will go

a) jack the car and set the frame on stands, let the suspension hang. measure C-C of caps

b) remove springs and jack the axle to full compression. measure C-C of caps

c) measure center of travel C-C of caps

d) measure 1/2 way between full compression and center of travel C-C of caps

e) measure 1/2 way between full droop and center of travel C-C of caps

you now have 5 measurements that map the arc of the rear axle through it's travel, where is the shaft the shortest? maybe even take another 2 measurements 1/2 way from the shortest point you found by the 5 points and the next closest both directions. you want to find the shortest possible shaft length, then subtract your desired safety distance for the slip yoke so it doesn't contact the output shaft. 1" is a mile, i'd go 1/2" maybe 3/4" max from known minimum shaft length.

pull the slip yoke out to your safety distance, set the axle to the minimum shaft length position and double check your calculation C-C of caps, order shaft. on a budget and i always am, hit the 'yard and buy a shaft longer than what you need and get it cut & balanced. i found an alloy shaft from a dodge 1500 2wd truck and swapped the yoke & new joints from my too short shaft IIRC