TH350 vs. TH400
 

which tranny would be better for a car with 750rwhp? what advantages does the 350 have over the 400? i am debating on what tranny would better suite me. any advise will be helpful. thanks

Well, if you look around this forum search for TH400 and TH350 you'll find lots of posts and ideas about them. The general consensus is that a 350 is good for lighter cars. It has a little less rotational mass but may require a little TLC every now and then. Most people, including myself, go for 400's due to their added durability. You can get the drums replaced with aluminum to get rid of the rotational weight argument as well. Beyond that you won't find anything significant beyond weight and durability.

can you get a lock TH350? which tranny is usually cheaper to install?

i would say that they will cost about the same to swap but honestly the 350 would be a little bit cheaper. not enough to make up you mind though.