Im swapping in a new 350 with about 420 horsepower (desktop dyno, so probably a little bit lower) How long will my stock 700r4 and rear end hold up. Dont laugh, but they have 200,000 mile on them. If i take it easy can i have them last a few months or no time at all?

 

They will probably hold up for a while if you drive like a grandma.I would be particularly worried about the tranny, it's probably on it's last legs and if you put 420 HP through it, bad things are gonna happen.