Update:
This morning I removed those damn 09-689 Pistons and replaced with the factory pistons/rings that I removed. Compression is back at 130psi. I compared both and it appears the factory units have a slightly larger dome to them. Now

I found the same issue as the original poster with these pistons. While troubleshooting my poorly running 1980 440 trailfire I ran a compression test, both came up at 130psi (factory pistons). I then came to realize the crank seals were bad.. So I broke it down to replace the seals and while I was i...