What was it doing to make you pop the top off it, I would have checked squish . What you had right there can run in the right hands. Most would consider it it a cobbled together. If it were me and planned on building something else later I would deck the cylinders and head for a good seal and put it back together , that look to be wang crank that I wouldn't put a wampus over unless u let me swap rods n bearings and just reuse the webs. Either way it ain't cheap , if your gonna order a cool head from Jeff 22 cc domes won't cut it on a 4 mil for pump need 23.5-24 cc domes if it were my motor I would deck the cylinders about .005 order .025 and .030 base gaskets 24 cc domes and noss head . If u need to clean the cylinders up let me know