Mothball the tranny and torque tube, put in a T-5, open drive line, disc brakes, tube shocks, modern tie rod ends, electronic ignition, and radial tires- and if you, or a future owner, ever wants to go back it'll be easy to do. In the meanwhile, the few hundred you save not rebuilding the original engine in favor of a v-8 won't make that much of a difference to you drivability wise. Upgrading your suspension to deal with the extra V-8 power would make up for the difference in cost pretty quickly.
