Best way to reduce compression ratio?

the difference between 91 & 93 is not that huge... those are all estimated measurements anyways.

second clue is 10:1 is not too high. you should not be "detonating" at all.

my guess is you have an ignition problem. :D

misfiring / backfiring could be caused by several things...
so the real fix is to get the car to someone with the tools to check timing/dwell/etc.

also I like this chart. I know people don't like champion plugs but this is a nice little guide ;) it says carb but it includes ign stuff

[ame]http://www.championparts.com/carb_troubleshooting_guide.pdf[/ame]