I've used the adapter on four 235-261 engines.Like said above,it fairly easy to do if the engine is on a stand,a little tricky trying to drill with the engine in place,radiator removed,but possible.
The 216 type water pump is designed to be driven about 1.4 times the crankshaft speed.The 55 and up pump is underdriven,slightly less than crank speed.You may want to fidget around with pump pulleys,a 60's Falcon 6 pump pulley is the right diameter and depth if you're using a 3/8 belt.Takes a little engineering to do this.Watch the fan speed cause an old fan may not like being driven faster than is was designed for.I used after market paddle blade flex fans,easy to trim the blade edge for damper clearance if necessary,and they are rated for 8000 rpm pump speed.
I had used the short pumps,the engines all ran hot when caught in traffic cause the fan is too low.With the adapters and higher mounted 216 pumps,never got hot and even ran a touch cooler driving at road speeds.
