Was the car originally a v-8 car? If so that makes things somewhat better. You will have 5 lug hubs and heavier springs. If you are thinking of adding serious power to a '65 I would start by spending $800-$1000 dollars on a power disc brake conversion for the front or at least manual discs because the drums are a borderline safety hazard with vintage power, and downright deadly with modern higher horsepower engines. I'd also spend some bucks on upgrading the suspension and firming up the chassis. Then I'd probably look for a 5.0 HO from a late model Mustang or Lincoln Mark VII. Also if you can swing it Ford Racing sells a complete rebuilt 302 with aluminum heads that's advertised at 340 HP for under $4000 that a very solid option. All that said I'd definitely start with brakes and chassis. Also check very carefully for rust. These cars are never as rust free as you think they are which poses safety hazards all its own.