Im building an estimated 650hp 383, and I was planning on a th400, but my engine builder would rather use a 350, says they hold up and the 400s take more power to turn. This car will be beat so I'd like something sturdy. What do you guys think? Manual valve body, reverse.

 

Your builder is right about the TH400 using more horsepower to turn.The TH 350 can be easily built to handle that amount of horsepower and it's noticablly lighter and smaller than the TH400.Even the 700R4 can be built to handle that and you have overdrive for highway use.

 

a friend of mind has a 70 chevelle and drags steady with it. he has around 700hp and has trashed a 400 tranny twice. Build what you want to but if street use is more probable than not 3 speed trannys are not fun at 70mph. If the tranny whichever one is thrashed on alot failure will eventually occur with any of them.
I like my 4L60 level III from gearstar the low gear of the 4L60 is awesome along with the overdrive.

 

Its not a daily driver, really a weekend bruiser, dont care much about od, but it would be nice. It's also carburated and its not going to be good on gas any which way, so......