I bought an 85 because I could afford a nice car with good body and interior, whereas if I bought an 87, I would have had to buy one that needed a lot more work or was worn out and tired. I thought the 85 HA setup would hold me over performance-wise, but after much consideration, and wanting to go faster easier and cheaper (my first opinion, no offense to anyone), I decided to convert. I bought most of my parts from a vendor here on the board. You can slowly collect them if you want, buy them all at once for about $1500-$2000, or just buy an 86-87 car and be done with it. It is all about the $ with these cars, just depends on what you have, or want to spend.
Some items you'll need:
wiring harness
ECM
MAF
pass header
pass valve cover
intake
dog house
throttle body
front bracket
alt
PS pump, reservoir, bracket
turbo
downpipe
crank sensor
cam sensor
electric fan
radiator hold down
hard coolant lines
intercooler
up pipe
clamps and hoses (IC)
upper rad hose
heater core selector valve
heater hoses
coil pack and module
tranny dipstick tube
oil dipstick
cruise cable
throttle cable
etc, etc, etc