I've swapped out 906's for 915s with a good comp valve grind on several different cars. Usually improves et by 0.5 sec., and 5 mph on a typical, stockish street car. It is so much fun, I keep the heads around and let people use them.

On one version of my 440 I ended up with 10.3: 1 CR and it would blow about 200 psi on the gauge. Would not run on pump gas in the Charger/3.23/stock converter.

175 and pulled timing, I could see that working.