Thanks for all of the information fellas. I went with the slotted screws and am super happy the factory had the foresight to put 'access holes' in the crossmember to tighten the two screws closest to the back of the truck. I also made a cork gasket for the bottom half.

See pic.
Pic of two piece trans cover

"My tires and tubes are doing fine, but the air is showing through" smile

1946 Chevrolet 1/2-ton
In the Stovebolt Gallery
More pix on Photobucket