I did the same thing, My 69 Z has an LT-1 and although I havent used it in years I use to drive the living piss out of it and the original motor is on a stand...Im about to have the car restored and Im leaving the LT-1 in it...As for original motors I am doubting how many are actually real and not restamped, those motors were not totally bullet proof and the big blocks use to eat valves like crazy.
You didnt order an L78 or 427 camaro to drive to and from work, you raced it and racing eats motors if done correctly.