Hello, I got an 84 chevy pickup 1/2 ton and a 402 big block and was woundering if it would be a wise decision to put the 402 in or would i have problems in the long run with braking parts on myTruck?

Your not really having fun until you break something, throw her in.

auto tranny. should be fine for a good while

ya untill i brake some thin i got a 350 turbo but i dont know it will hold i cant find a turbo 400 for 4x4

It will be fine. should bolt right in and everything should wire up the same. if your using manifolds the outlets are a little larger so you might have to up grade pipe size.
everything like flywheels ,distributor,starter are the same.

you might want to up the vaccum modulator to a new one so it keeps good clutch pressure.