Hey Steve, I'm no expert but I think if you set your cog at about 35% same as your gasser you'll be fine and as far as the pipe and header length I would start at 9 1/2 and work back from there. and yes measure from the plug down the centerline to the widest point on the cone. This should get you close but I think you'll find you end up around 8 3/4 give it a shot let us know how you make out.