I will straddle the fence on this one;
On the one hand, if you have always wanted a hemi vert, then build one and check that off the list. Just don't butcher the car doing it. Keep the original drive train for later or the next guy (hemis fit in a lot of cars...)
On the other hand, while putting a hemi into the car would be cool, actually having an original car will probably be more valuable in the long run.
Bottom line - do what you want as it is your car. If you REALLY want a hemi vert, here is your chance. If you keep the original drive train you are not out anything and if the hemi doesn't work out for some reason, you can sell it and then make the car original.