Farmall cub coolant in oil

I have a couple problems. I have a 1953 Farmall cub we rarely used, so figured to sell it. It sat over the winter. Went out today to check oil and start it. Dip stick was 2 inches above full. Took oil pan plug out and straight coolant, about a quart flowed out and then the oil. I don't know much about engines but know this is bad.  I want to sell this like I said, but don't know how to fix. Question is should I find a fix or not. If not then how do I list this tractor not wanting to screw anyone? Also, how do I price it? Thanks

Farmall cub coolant in oil