How much timing can it take

depends how low the compression actually is...... I run my 318 at 20* initial and 40* total. No pinging, performs the best, starts great. Been this way for about 6 years now. However, if you are at 42* total, sounds like you are at the upper spectrum. If I were in your place, I'd see if it liked a couple more degrees of INITIAL, curve it all in by 2800 rpms, and set the total to about 38* and see how it likes it. FBO plate is your friend.