To Build Or Not To Build

Well actually, I've decided to replace the engine, at least initially. The car in question is a '70 LS5 with about 85K miles on it. Circumstances dictate either building the original engine or put in a reman. In order to have some fun with the car before winter hits I'm going with the reman. However, would paying the core charge ($900) be worth the price just to rebuild the engine later and put the original back in the hole? Would the original engine increase the value of the car enough to make it worth while? I referring to the hassle of the rebuild and swapping the engine twice. Opinions would be welcomed.Thanks,
Stan