Tech: Pontiac Engines

Those manifolds are pretty nice, can you buy them new?

 

I have a pair of originals on my ‘31 Pontiac. They look great and fit nicely between old narrow frame rails.

 

I’ve just finished assembling a Tri-Power for my ‘59 389. It’s a 1960 SD manifold 535552. I have a (big, ugly) ‘59 Tri-Power thermostat housing but my manifold has a second hole next to the thermostat hole approximately .75”in diameter and the thermostat housing only partially covers that hole. (?)
The hole is as-cast, not machined or threaded. It looks like maybe it feeds a bypass fitting on a different thermostat housing. The ‘60 housing listed on eBay doesn’t look like it covers the hole either? Can anyone tell me which thermostat housing I need or what should be done to either block or utilize the .75” hole. Obviously, I can plug it but I’m not sure if that’s the right thing to do. I’ll post pictures tomorrow. Thanks in advance.
Added pictures. This is the hole.
View attachment 5262179

 

You can see in the previous photo that there is another strange hole with two 1/4” bolts that I’ve already capped, what was that for? It isn’t there on my Offy 2x4 manifold but the 3/4” hole next to the thermostat is there. Need help from the Pontiac gurus.
The Offy intake…..

 

Being cold and damp all day and having a minor attack of gout in my ankle I decided to stay in and scour the internet for info, (and catch up on a few HAMB threads I’ve fallen behind on).
So it seems that the 1960 Tri-Power manifold is a one year only with a one year only thermostat housing. It’s not reproduced. The .75” hole feeds a bypass fitting and hose that runs to a fitting in the top of the 1960 water pump. The ‘59 389 didn’t have any of this. The two bolt boss was for some kind of thermostatic switch for the factory vacuum secondary system. Mystery solved. I’ll tap and plug the hole and use the slightly more attractive ’65 thermostat housing.

 

I just read about the 303 that Pontiac developed for TransAm racing and the 366 for NASCAR. Both had the new heads with equi-distant exhaust ports. Are these pictures of them? I read that they tried to get corporate to use them as the base V8 instead of the 350/400 but got shot down.