I left quite a bit of the flanges under the base of the cylinder untouched. The cylinder is held on with only 3 bolts, so I wanted to make sure the base of the cylinder stays rigid. Otherwise, I trimmed off the rest of the crankcase webbing as much as I can muster with my little 3" cut-off wheel. I wish I had a millling machine, but the air tools do an adequate, if not pretty, job. The crankcase only bears the load on the crankshaft bearings so there's plenty metal there even if you trim off all the webbings.