How often do you intend to remove the timing cover without disassembling the rest of the engine? Stovebolt timing gears last about 3 days past forever- - - -I've seen 50+ year old ones going strong with minimal wear. The timing cover seal can be changed from the outside without removing the cover. If you simply must make a change for some reason, why not tap the main bearing cap for a 5/16" helicoil and simply drill the threads out of the timing cover for a 5/16" bolt? The hole in the main cap is just about the right size for a helicoil tap already. I can't seem to dream up a good reason for changing from the original design since removing the timing cover is done so seldom.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!