sb tuning problems

360/408 sbm
360-1indy heads unported
10.28 comp
Solid roller 245/245 612/612 108 102.75
34 total timing i think around 14 initial from memory
Was around 10" vacuum at idle 850 -900rpm
1050 quickfuel raceq
Using bcpr6ey-11 bgk plugs
Msd ignition .

Although i like to open up the throttle a bit. The car does see a lot of cruising rpm 1500-3000 and idle time.

Problem being after driving for 20-30minutes the engine wont idle rpm slowly drops down to 500rpm and then will stall at lights.
By this stage the plugs are fairly black.

Questions ? Comments ??