i doubt that pro comp heads would drop the fly horse 100hp... especially sense i will be taking them to get cleaned up. that seams kind of ridiculous seeing as the procomps are much better than stock or gt40p heads and ported gt40p heads would probably produce about that power wise with a 393 stroker kit. What i have heard about the procomps is that there is a lump in the exhaust ports that effects the flow which can be grinded down.