I've got a '62 261 in my '50 and it works nicely, you just have to deal with the water pump and mount the oil filter so it doesn't hit the steering box. I made my own short water pump, but if I was doing it again I'd use the adaptor plate to put a 216 water pump on it, I had to use an electric fan since a mechanical fan sits too low in relationship to the radiator compared to the 216.
I'm about to tear it out and go with a 302 GMC I'm building, though. The 261 was fine but the one I have is tired out and burning a quart of oil every 200 miles. The Jimmy motor has more cubes and a much better combustion chamber design.
