Thanks for clarifying Rob.
I believe the benefits would be minimal on this combo, it wouldn't be worth the effort trying to tune it, you'd be fighting an uphill battle. V.A. is essentially a controlled vacuum leak.
Generally, vacuum advance adds timing at part throttle/high vacuum/cruise situations. Why do you need that here? If 'ol Skep is driving his car on the highway more than not, well, the combo is probably not the greatest for that.
In the case of my truck - a heavy vehicle with a low-geared, wide ratio transmission and highway gears - I have relatively LOW cylinder pressure because the P.O. put a large duration cam in a stock, low compression short block with the pistons a mile down in the cylinder. Heads are open chamber with a high-rise intake. The tune requires a bunch of initial timing to get it to run OK and under under a slight load it pings and stumbles like crazy. I messed with it to no end and tried my best to find the spot where it liked it but in the end it was not worth the hassle.
Only thing I could say is that perhaps I could put some heavier springs in the distributor to slow down the advance at low RPM under load but that's another Catch 22 that's probably not worth the slight gain in mileage.
