I have found in my old stash of stuff some new in the box perry fuel pumps to fit the St 51-56-60 , Veco 61, and St 40-46. Since some folks like to run muffler pressure on the stunt engines, I thought I might give these a go. Any of you guys ever tried these pumps before, for a stunt application?

People have tried them and complained about the weight.  Also, the backplate style of Perry Pump has some sort of bleed hole in it that has to be postioned properly.

It's also a bunch more finicky parts to keep clean and wear out.

That is interesting because one of the perennial debates    is whether the 4-2 break is caused by the engine going lean because its nose is up and the tank head is now lower, or the increased load on the engine because the rpm drops because of the larger load going vertical (engine heat goes up). Your observations (assuming they were in-flight) supports the first view.