You'll probably find that using a 35 coupe for Targa, you'll have to fit all the Levin bits to make it as close to a 'genuine' TE37 Levin as possible.
That means, badges, tail lights, flares, fender mirrors and that sexy grill and bonnet!! It'd have to look just like a real Levin, and run the equivalent engine... a 2T-g.
Ideally, you'd be better off to go for a KE15, or a TE27, as they had more racing pedigree and history than the 3x models.
As was mentioned before, it'll cost you at least 15-20k. And if you really want to make a decent, competitive car, you'll need to spend that 15-20k just on the car alone!!