Intake Manifold Water Leak

I installed a Ford Performance Z2 head on my 1973 351W.

My stock 2bb intake with EGR casting had 12 bolts.  A friend gave me a 1970 2bb head that doesn't have the EGR casting.  It has 16 bolt holes.

Since there is no threading in the heads for the extra bolts, those intake bolt holes are open.

Finished putting the engine together, cranked it - everything fine.

Started filling the radiator, and coolant started coming out of the rear open hole (2nd to the last bolt) on each side.

Any ideas?

I thought I read somewhere that you have to tap the 2nd to the last hole, and install a bolt???

Thanks.  

A very close examination of the ports (etc.) are exactly the same as the OEM head.

I'm sure I would have the same issue if I had used the stock heads.  After the leaks, it flashed on me that I remember reading somewhere to drill/tap the back 2nd from the last bolt holes, and install bolts in them.  I just can't remember where I read it.

The intake manifold p/n: D1AE-9425-CA