HEI will have a huge cap. Points will have a small cap. Besides that, if you peek inside, the contacts or points will be plainly visible on the breaker plate. The HEI will have a set of timing teeth, the points will have a cam.

I think dude before meant to say if it is EFI then wiring could be a problem. If it is EFI ( electronic fuel injection ) then the easiest solution is to swap the entire wiring harness from the donor vehicle.