Axctually in your case a shorter rod might be less detonation prone if you're hard set on 87 octane.

I'd look at a later magnum style crescent chamber head with about a 1.94" intake, a performer RPM and a vacuum secondary carb tuned a little on the rich side. Hydraulic roller in about the 230/236 @ .050 range. Keep the motor cool as possible, big radiator, big trans cooler independent of the radiator, keep the motor under 180 degrees. It may be tough to find an optimum ignition curve but the 3.91's should help.

I'm thinking hard of converting my little 341 into a high compression but high efficiency motor that should run 12's and still deliver well over 20 mpg using a late model od transmission in an early A body.