is this a stock 400 with open chambered heads? How soon/serious are you about replacing it with the stroker? As said SCR is where you are hurting. you could mill the heck out of the open chambered heads or get a set of 516 iron closed chambered heads & home port em (tho you are in Germany/not sure what's available there) & as you know it would not be practical to ship some OE lo po iron heads. You could go with the alum heads with the smallest chambers & adv the oe stock (I'm assuming) cam 4 deg & dial in the dist subsystems then transplant the alum heads when the stroker comes together.