What you are going to have to do is search based on your engine/carb combination, so if its an AQ 271 I'm thinking it is a 5.7 with a 4bbl carb, correct?
I don't have part numbers you're going to have to look for parts for similar engines (OMC or Mercruiser) that used the same Prestolite distributor.
I did some looking around, these parts are very hard to find as you have found, it might be best to quit chasing ghosts and upgrade to an electronic distributor. I was able to find them for my old 4.3 4bbl a few years back, mine are still good though. The Prestolite had a lubrication wick in the distributor shaft and you could pull off the rotor once a year and put a few drops of oil on the wick, lubing the weights and springs. That's what made mine last this long!
If I really wanted to keep the points distributor, I'd get some aftermarket springs and an advance timing light and experiment, you might get lucky and be able to do it that way. Here's my Sears Craftsman timing light from the '80s no doubt. You have to run the engine at the specified RPM, set the dial to the total advance spec # and it should read zero on the timing tab.