OK hit me with it guys. I just swaped a basically stock rebuilt th350 for a rebuilt basically for towing in a suburban th400 I looking at a 4000-4500 converter and I wanna put ina manual vavle body and trans brake what else should I do to it before I install it so that it will hold behind a 650-700hp 468 in a 3650# car that I want to run 9's in the 1/4 help please as Iam a very confussed several local club members said I should have kept the th350 others agree I will need the 400 well what do you guys think did I do the right thing and what do I need to make this thing hold up in this heavy of a car running that much hp.Also a local trans shop told me to get a power glide what do you guys think about that aswell I could get one for a decent price with all new parts and a trans brake already in it.
Thank You
Jeff

For a heavy car a t-400 is the way to go. I would not put a glide in anything below 1000 hp or over 2800 lbs. Picking a stall speed for the converter is not as simple as I want a 4-4500 converter. I will give a guess that you will need a 5500 converter with the cam you were looking at from Harold. As far as internal mods I am not a trans expert. Mine was built by Trans specialties in PA. But I can tell you that in your range, stock internals are adequate, however clutch setup and casing mods are where the changes are.

I've done the same , still wonder if it's right.
350 lighter , better shaft angles can be upgraded to 36 tooth sprag.
400 only have 34 tooth sprags in 69 and 70 years. Then you have to do the upgrade to a 34 tooth sprag.The 400 use 8hp more supposably.
Probaly does'nt make much difference once you update the sprag.

I have an upgraded heavy duty TH350 in my 460 works great.