I know you came in here looking for advice from experienced mustang folks. Both guys above gave excellent advice. If you spend, for example, $8k on everything to do the swap, or spend $8k on a whole V8 car which would you want? I'd want the original one. Those are made up numbers but you get the point. The difference is you don't go insane trying to find every wire, plug, bolt, etc, etc, etc to get the pile of parts working.
If you are thrilled to do all that then, hey, nothing wrong with a project. I've seen lots of those types projects sold later on after the owner waved the white flag. Seems to be a lot of trouble for a less than desirable donor car. You'll get good advice...up to you. Welcome to the forum.