Kelly Jones

am picking up a uk classic later today with 127k miles and am thinking an engine rebuild isn't going to be too far off judging by the amount of bottom end failures these cars have.
i would like to buy a used engine and refresh it before swapping it over, ultimately i would like 350 - 400bhp so would like to know which engine is the best to go for. As i understand it with my limited knowledge an sti v9 engine has the best internals and would be fine for my power needs, if i buy a complete sti v9 engine, would it be a straight swap for my existing engine? what parts are worth changing while i am rebuilding it? head gaskets, rcm oil pump, arp bolts, cal bearings etc....anything else?
Also what car had the sti v9 engine, is that a hawkeye jdm sti??
Apologies if i am asking questions covered before