I have an L98 bored 40 over, with no cats, no smog control, 3" exuast, flowmaster muffler, exaust dumps, 1.75" shorty headers,
descreened mas air flow sensor, k&n airfilter, and I did the coolant hose of the throttle body trick. I was wondering what a suggested base timing would be at 4300ft above sea level. The sticker on the car say 6* btdc. Oh yeah and the heads are milled.

 

You are going to need to play with it and watch your knock counts as you datalog (see DIY PROM board). Not all knock is audable and you may be running too much base timing without you knowing. Your motor is at the point where chip work would be worth its weight in gold.