I'll have a crack.. I have one in my car -- 1152, ported '295 head, unknown but lumpy cam, LCBs, 2x HS2's, 10:1 compression.
I don't have the 123 manual in front of me, but the way I set up mine was to firstly choose the group of four curves most appropriate to my engine using the manual as a guide. From memory it was numbers 5-8, but I could be wrong there.
Once you've chosen the curve group, start with the least aggressive advance (lowest number), static time the dizzy, then go for a drive. Put some load on the engine at ~ 2000rpm in top gear and listen for pinging -- if it doesn't ping, try the next curve up (more advance). If it pings, you've got too much advance and you should back off to the one lower.
You should be able to feel the difference between curve groups in the seat of your pants, the throttle response will be better in the correct group and it'll develop more torque at lower revs. Once all the advance is in at revs, they'll all feel the same.
Hope that helps!
