here are the rules we have been using,.030 over bore,stock stroke,stock length rod but may be after market..310 max lift at the valve.Stock diameter stainless valves,champion rockers allowed.porting is allowed but you can not touch the seats or the inlet of the port on the intake side or the outside exit portion of the exhaust side.any valve spring,any stock configuration head gasket.any tillotson hl series with .880 ventura.flat top Honda piston is allowed.billit flywheel,stock ignition.exhaust max length is 22 3/4.any fastener as long as stock diameter is maintained.sealer is allowed on head gasket,exhaust gasket and valve cover gasket.we used the animal rules to come up with most of these rules and have found them to be very competitive with animals and flatheads.we ran this combo at Batesville in the unlimited class and qualified 6th.we were running 4th when got knotted out going to the flag.i don't know how well the combo will last but right now it looks to be very durale as well.hope this helps