There is nothing to it as long as you are willing to completely change the steering system, modify the front suspension crossmember, change the front springs, rebuild the firewall and transmission tunnel, cut exhaust pass-through holes in the front cruciform arms and notches in the rear cruciform arms, change the brake master cylinder location, fabricate or find motor mounts, build a new transmission crossmember, change the driveshaft and rear axle, change the radiator, relocate the battery to the trunk and a few dozen other things and that is to use a small block Ford V8. Using any other engine will make things complicated!
Chuck Ingram can probably add a bunch more issues to the list.