It should be same as a 350 on the higher end, not as much as the 400.Approximate numbers: I used to have these numbers written down somewhere. There are some valve body changes that can help reduce hp loss as well.
Powerglide: 20-25 hp
TH350: 30 hp
200R4: 40 hp <---A well built one will do you fine!
TH400: 45-50 hp
700R4: I can't find anything definitive. I've heard people claim 50hp