I'm sorry that you have to sell this piece of family history. It had to be a hard decision. I agree that it would be a shame to change the engine . At least these Sprint cars are starting to get some respect for what they are. This looks like a solid car that could be enjoyed as is or would be worthy of refurbishment if not full restoration. At your asking price it should sell quickly. Good luck with the sale.
If I had this in my garage I would put a five-speed in and keep all the original parts on a shelf .