Several options boss internals, local machine shop balance rotating assembly aftermarket internals, local machine shop build / balance aftermarket short-block (which vendor) L&M seems like you should have sleeves too by the time you pay? (AKA) kinda expensive. modular head shop has a good looking site for parts, and short-block, but have heard horror stories local machinist is good, but afraid of the wait with everything apart for too long, but price-point is good, and no extra lump of Coyote short-block sitting around taking up space. So what did you do, and would you do it again? I posted here in power adders because of CPR coming hopefully soon!