Are you considering the whole package, headwork, oversize valves, flatside carbs, adjustable timing, big bore jugs, cams, hi-compression pistons, etc. as there are a lot of levels and variations, it's hard to answer your question unless you provide just how far down the rabbit hole you want to go, not to mention what you can actually afford. Spec it out and you will get the feedback you desire, as almost every performance enhancement available has been explored by one or more members of this forum or over at the R.A.T. site.