well im putting an sr20de in my starlet and i would have to say its not hard.. just time consuming and requires alot of thinking.
the way mines set up the enigine come past the firewall for better wieght dist, even then theres no room really for a radiator behind the bonnet crossmemba. im tossing up between a twincore ek civic radiator or a cutom made 3core.
engine mounts are easy
gearbox is a bit of a pain as its soo long. you do have to cut the tunnel as the gearbox has sticking out bits and the starter hump. not sure about the dets but the de headers poke into the cockpit.
steering is fine but you will need bigger front brakes at the least.
im doing al the work myself or getting help from my brother and cousin so its not costing much.
in short do it to the 85 much easier.