Dakota,
My jeep with a 6 in it was something else, got cr*p mileage and it was a pain to work on let alone ended up on the side of the road many many times. I dumped it for a MB38 and that lasted 5 years before it rusted away and it had a tried and true F head Jeep engine in it.
The Ford 6 I had leaked coolant into the oil, even Ford looked at it and they recommended a head replacement but that didn't solve the problem. With 140k on the engine, 110k with the new head, the trans gave out and I sold it. I heard it made it to 250k before the engine finally cr*pped out. Since the head was replaced, I hoped it would die with coolant in the oil, it kept going and going.
Slant 6, good engine but I prefer the predecessor, the flathead 6. Now you would think that you could still get parts for the slant but I looked last year (had the chance to buy a 1968 Barracuda with a slant in it) and didn't see much. But I still can get most of the parts for the flathead 6 - go figure.