well most likely for the overheating it could be a blown head gasket ( i believe with $1k spent on metal head gasket, arp head studs and proper machine work and assembly you will have a reliable motor)
hoping that it's just old crusty serviceable things like the thermostat, radiator cap, water pump & clogged radiator you can also solve the overheating (hopefully)
the 3.0 supra does go extremely well... and i would suggest saving some bikkies for that head gasket
find out from the old owners if they have had it done yet? if they have then find out what torque they did the head to... hopefully you may get away witha retorque..
let us know what you find out etc