I am going to be doing some big power upgrades and am looking to see what other have done to improve brakes and suspension? are there swaps from other vehicles i can do? I will be going to around 350-400HP and later more... so I need to be able to stop and not float down the road. I have a 85 F-150 supercab long box 2wd.

 

brake upgrade would be switching from rear drum to rear disc brakes.

 

Would that be possible on that year chassis? Would adding a complete F-250 or F-350 system be doable and/or practical?

 

well, if you have the parts it is a bolt on deal.
many many many people over the years have done the gm rear disc swap.
a 99 and newer dana 60 van rear axle is a bolt under if i remember correctly.