You've got me interested now Rexy. I'm expecting 450hp or thereabouts out of my 377 SBC. It'll have bulk torque too being a 3.75" stroke. The TH350 I have is not really good for that much, it is really just a heavier duty rebuild on a standard one with a B&M holeshot 3000 converter and a B&M shift kit. I plan to use it to get the car sorted and Engineered, then I was going to get a new one built to suit with a better converter like a V6 4L60 converter modded.
But after I did some research today a TH350C might be a better option. I found a good case and converter today, the rest of it was scrapped though. So I just have to look for another box for the valve body and internals, but I can look for Pontiac ones too as this case is good. The lockup looks to be verily easily controlled using a vacuum switch and a relay off the brake light circuit so the converter only locks in top gear and high vacuum with brakes off. It just needs a 3000rpm converter built from a 4L60 with the TH350 pump snout on it. The rest of the internals of the box other than the extra bit of valve body for the lockup is the same as a TH350. Will make the car far more tolerable on highway cruising with a 3000 or higher stall and a 3:1 or 3.25:1 rear end.