its do'able, but a lot of heartache. i was going down this similar path myself, just like you i have all the parts available from a donor/r&d engine but the more you figure it all out the harder it all becomes. it would be a waste of time unless you upgraded to the gd sti tmic aswell, but then unless you went a spec c intake manifold to bring the tmic off the firewall but because its the phase II motor, the manifold wont fit without major surgery.

anything is possible with enough vision and time, but a nicely tuned version iv sti with the right breathing and tuning mods is fun enough, after all you still have the spec c to play with!