Each Nasty Boy will present different challenges reverting back to original. Some are more highly modified than others. It's easier to make a modified car by removing lots of vital parts than it is to try to preserve as much of the Healey as possible. I'd be leery of trying to bring back a car with a lot of chassis mods unless you're ready to spring for a new chassis. Also you need to check for any chassis twisting from overenthusiastic launches. Here's what I'd look for in evaluating a potentional car. Try to find an old conversion without the motor and trans, these sometimes go for short money on eBay. A Ford conversion takes less room than a Chevy, so that would be preferable. Look to see how the motor mounts were handled, sometimes the Healey ones are torched off, making problems later. Check the chassis for any alterations. Sometimes a Chevy conversion will involve notching the chassis for clearance of the starter which would be a negative. The footboxes will be narrowed in any case, Chevy's more than Fords so plan on rebuilding them. Check the transmission mount that you'll need to remove. The tunnel has also been modified, thee question is how much. The rear axle has probably been replaced, see whether the suspension and shock mounts have been hacked. If the car ran headers instead of iron manifolds, there may have been mods in the front chassis area, check for them. Those are the main things I can think of, but converting to a V8 can also mean a lot of little mods, too, like throttle linkages, radiator mounting, clutch linkages, etc. Like evaluating any prospective project, it's all in choosing the right car and choosing the wrong one could be very expensive. However, I've seen some pretty rusty stock cars brought back as well. When I did my conversion, I tried to do the fewest modifications possible to allow someone to convert it back if they wish. Take a look at my build to get an idea what mods will be done:
https://forum.britishv8.org/read.php?13,8264