I have no clue the value of your car or what changing the engine would do to that value. That said you could pull the original engine (after fogging it with
oil), then properly store it, so it could be put back later, thus preserving the value of the car.
Now you can install another engine for fun. However to keep with planning to re-install the original engine some day in the future, you need to minimize changes required to fit the new engine.
That would tend to make me go for a 347 stroker. If your budget would allow, I would go with an aftermarket 4.125 bore block which gets you a little over 360 cid. Go with the best heads you can afford and keep the cam more to the mild side. You should be able to make somewhere near 400 Hp and still get decent MPG.
Is the car EFI now? If it is, stay EFI. If not, stay with a carb.