Keeping the 250? Do a T-5 swap. Plenty around, inexpensive, and will be able to take a 250 unless you start getting some heavy modifications.
With the car being a '68 Camaro you should have no trouble finding the parts to do it, or people who have done it before. Probably one of the most modified vehicles ever. A few Google searches will lead you well on your way, and any T-5 related questions can probably be handled by a few members on here.
