Thank you Ted, you cleared it up, the 3/8-16 is what I thought and I had read about the length of bolts somewhere but wanted it confirmed, again thanks.

If you’re talking about the single vacuum port at the back of the ECZ-B 4V intake manifold, then that is a 3/8 NPT thread (tapered pipe).  If you’re referring to the threaded bolts holes in the heads behind the intake manifold, then those are 3/8-16 threads.  It’s important for those two holes to have short bolts as those holes go into pushrod holes and if the bolts are too long, they can contact the pushrods and bend them.  See if this picture helps.
 

Lorena, Texas (South of Waco)

I thinks it's 3/8 pipe thread. 


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

Further information:  Pipe threads are tapered.  -IF they were not, they wouldn't seal.
Hope this helps!   


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

If it's the vacuum port a bolt won't work, it's pipe thread. They make plugs for it most hardware stores have them.

looks like these ports are threaded, does anyone know what use they are and what size bolt it would take to seal the holes, I don't want to get a bolt too long that would mess with something in the engine, also thought this topic had been covered, been about 2 hours going through post for information, found one post where it was use for brake vacuum but not sure. I think I need to put bolts in them. Thank you!!