For vibration try the old bicycle style hand grips, as far as the oil leaks, if you use metal base and head gaskets, run a file over them to check for burrs and nicks, hang them on a coat hangar and spray them with copper coat. When you install the barrels and heads do not tighten any thing until you align the intake ports with a 30 degree triangle, touching at least 2 FLAT) places on each head, then torque them per the gasket manufactures spec not H D spec. You will not have any leaks at the base or heads, side note check the crank case areas good where the cylinder studs screw in and be sure of no cracks and the studs are tight, if in doubt replace them as they will come loose and stretch, a drop of oil under the head bolts will give the best torque