Q: Paul, my Lycoming O-320 B2A s/n L-504-39 looks like it has a hollow crank.
It also has an available accessory pad below the right magneto. And a 1/4″ plug on the right forward case in front of the #1 cylinder.
Am I able to run a constant speed propeller on this engine? It is on an Acrosport II.
A: Guy, from the information you provided, including the photo, I think you’re okay to use a constant speed propeller on this engine.
I’d recommend you review a copy of Lycoming Service Instruction 1435 and its Supplement No. 1. This should provide you with all the necessary technical information you should need to move forward with your project.