How to sqeeze out a little more speed?

Last summer I picked up a 68 barracuda. The owner knew very little about the engine build. Soo....I back tracked to the owner before him. And he didn't know much either. But betwen the two of them this is what I found out. (not to mention crawling around my car and doing a little research)
Engine is a 318 +.030 (total engine rebuild)
Cam is "a little bigger". One owner told me. lol
Edelbrock performance intake with a 750 holley on top.
340 exaust manifolds.
Stock 4-speed trany with hurst linkedge.
Stock 8 1/4 rearend with suregrip. (no clue on the gears)
Monroe air adjustable shocks in back.
Now running with BF Goodrich R245/60 R14 at 35psi.

This is my everyday driver/race setup. This weekend I happened to win in the trophy class at Firebird Raceway outside of Boise, Idaho. My best ET was 15.766. (never touched 4th gear)
My question is, what can I do to go a bit faster without digging into the engine? Such as lowering tire pressure, lbs on my shocks, type of engine oil, different spark plugs(autolite), etc......