Hello, welcome. I had that issue with my 1970 360 back in the 90's. The shim did help at the time but the engine was in need of a complete overhual. Since then I have had a rebuild done and cold I get between 65-70 psi and hot I get about 10-12. Thats without the shim presently and about 25K on the engine.
So my experience was that the shim did the trick at the time.