Wahoo40, The easy motor to replace the 216, would be a 1954 235 or 261 Chevy as these were the last motor with the 216 style water pump, easy deal. Those however are not easy to fine so next good motor is the 55 to 62 235, which will require mods to the water pump. Like truckernix said, read the tech tips.
Also you may want to get a catalog from Patricks antique cars in Casa Grande, AZ ,has a section on all the mods you'll need plus other neat stuff. his phone- 520 836-1117 or web site www.patricksantiquecars.com

Best of luck

It's easier to get forgiveness than permission!
1946 1/2-Ton Chevy
1953 Chevy 3/4-ton Factory Stakebed