engine upgrade

I have a 66 mustang with a straight 6 motor and want to upgrade to a v8. will it hurt the value of my car??? In other words , is it better to keep it stock?, or will the value increase with a v8?? I'm also upgrading the rear end and tranny. please give me your input to anyone who may know the answer to this question Thanks

thanks mrmustang I appreciate your input.I have one other question though. Why replace brakes and with what kind? Also the only thing I am currently replacing on the suspension are the coil springs. What else do you suggest? Upper and lower control arms etc were replaced about a yr ago. What other parts do you suggest? I appreciate your help> I have the car ready and waiting for it's new motor, rearend and tranny, so it helps to know now while the car is empty. Thanks again