Should I leave it Stock?

Well it's your car, do as you please. If it were me I'd do what I wanted and keep the stock parts to put it back or give to the next owner. What your wanting to do isn't all that radical. If your planning to sell the car at some point then just enjoy as is or sell it and buy what you really want.

Another option is find a 5.2 Magnum or 318 and build a decent motor and keep the stock 273 in moth balls. It really depends on what you want out of the car and your budget to get it there.