Why do you have the idle set to 1200 rpms? I have a Crower mechanical roller cam 641/636 lift and 256/266 duration at .050. I have Edelbrock Performer RPM heads #60559 with 315cc intake runners. My carburetor is a Holley 850 DP. My distributor is a MSD Pro-Billet 85561. I have my idle set at 900 rpms. My initial is 12* btdc and the total is 37*. Looking at that Streetfire distributor and the MSD 8428 advance kit they recommend there is really no easy way to set up the mechanical advance. Even when using a medium spring the advance curve will start with 8* @ 1000 rpms. The advance curve will be at 20* @ 3500 rpms and you will have to use a stop at this point. Even then you are looking at 16* initial 20* mechanical advance. You will have to use the vacuum advance stop provided with the distributor also set at 11*-14*. Try backing off the curb idle screw on your carburetor to see what the lowest rpm is. I don't want to piss you off but IMO that distributor is junk. It is to be used with a completely bone stock engine. A GM HEI is easier to setup for a performance camshaft.