I would unhook the vacum advance and plug it for now. Then get the mechanical advance dailed in. Usally you need to limit its movement for higher compression engines and give them more initial timing. Also helps to smooth out idle a little.
Not sure about how the proform comes stock but most do not come setup out of the box for your setup. This is probably your issue. Also have you tried colder plugs or are you runing the stock style.