Frank, here's a compressed gasket measuring tip. Buy two of the same kind of gasket. Cut off enough of one to provide a cover-case metal to metal measuring point, preferably for a vernier caliper, but I bet feeler gauges will get you close enough. Torque down the cover and sacrificial gasket and measure, leaving out any guts that could prop up the cover and pooch the measurement. I think a gap in the center of a fairly straight edge would give a truer measurement than a corner, and I figure a .25" wide V notch in dhe edge of the gasket is enough space. I've use this to measure compressed head gasket thickness. Kid's modelling clay has been useful for measuring stuff like piston-valve clearances and squish volumes, and could check shaft-cover clearance in a case like this. I set the minimum clearance on the depth part of the vernier caliper, and punch test holes in the compressed clay at the point of interest. Any test hole without the full rectangle imprint of the end of the caliper beam is too damn tight. I neglected this step once on a 301/2 SBC, and at 8000rpms, the piston finally tapped the valves that were at long last floating or bouncing off the seat, bent them and stuck 'em open, and those nice new MT titanium rods sawed the block into pieces, literally. Took the motor out in about 8 or 9 "big" pieces, and too many little ones to count. It made an impressive (and expensive) sound when it let go...