I found out a few things that are worth mentioning here. Take it or leave it.
If you have a 216 engine to look at, you will notice the fan is about centered on the radiator. The truck was designed that way for a reason. If you put a new style 235/261 motor in your AD era truck, after you have figured out how to put a shorter shaft pump on it, you will notice the fan is 3 inches lower than the original 216 setup. Air actually gets pulled from UNDER the radiator with the new engine, causing a POSSIBILITY of overheating.
This is where a gazillion opinions yay or nay come up on if that's a real factor. So, if you are building a new restoration, Pre68Dave has a great adapter plate that moves the water pump back to where it belongs and eliminates the entire issue. So if you are not sure, err on the side of caution and pay the $50 to save wear and tear on your radiator, engine block, etc.
The other issue is the dual pulley HB. BOTH of the standard air conditioner add on companies that are popular think its just fine to have one pulley on the HB, then two pulleys on the AC compressor, running one pulley as your current system works, and the other one to your alternator. So, when your compressor fails, your alternator is just as dead. I do NOT like this idea, so feel that a person needs a dual pulley HB. The HB I have found that has two pulleys and fits right on your new style 235/261 crank is from Vintage Air and its over $400. My good friend Jerry.. Hotrod Lincoln as he likes to call himself on our Chevy forum for some god-only knows reason.. knows his stuff and is working to resolve this problem. I am very hopeful his solution is the answer! Thanks Jerry!
Real answers for some of your current needs on these trucks are few and far between. This one really matters for a lot of people out there.
