1967 Mustang Fastback help!?
As in you only have a body and nothing else? Or you have a roller car with no drivetrain? Or you have a shell, no drivetrain or interior?
If you have just the body, then you're going to need more than 40k to build a nice car.
If its just a roller, put a 9" rearend, 5 speed manual transmission, 347 stroker motor.
If you need and interior too, the hardest parts will be the seat frames, dash, steering column. the rest any decent mustang parts supplier will have.