I've been looking at all the different threads and pics on guys doing thermostat and head gasket replacement and was wondering why you can't put a thermostat in the manifold because it looks like it would take one?

 

It will work. You need a machinist that will take on the task, a conventional GM Tstat and housing or maybe even the D1 stat and housing. It's on my list.

 

It looks like on some pics I've seen that it has the step down for it to sit? I'm planning on doing my head gaskets soon so I'm planning on looking into doing this mod and possibly either enlarging the water hole in the block or a smaller hole below to allow more flow

 

I put the traditional stat up to the opening for the elbow pipe and it looked like it could be done, that's all I'm saying. Even if a bead has to get laid down then milled out for a recess its still doable with a decently equipped shop.

 

I'm looking forward to pulling mine down to see how much trouble and cost it will be. It would be great to have a normal style tstat in place instead of that way over the top system they have!
But like you say it's finding the right people to do it and do it right the first time. I am wondering if it would also work if an insert was fitted to take one of the smaller style tstat but the concern would be enough flow!

 

Just take you a GM 180 Stant Superstat and a GM Tstat housing that necks off at a 45 deg. I'm even going to get the 45 deg that rotates 180. Have some options and variety stocked up so that a machinist has plenty to work with. This is that project where you want a lil bit of everything so there are enough pieces to make it work well right out the gate. I'm talking about stats, housings, Orings, gaskets.. A sackful. Last thing you want is a phone call asking YOU 50 questions. Hand it to him and say "call me when it's ready."

FYI, these intake manifolds are on eBay all day long anywhere from $10-$100. Just leave your original in place and buy a 2nd for the machinist.