Finally found some M3 and M4's today. A few of the M3's in the box I tried did fit the Western Dig but most did not. For some reason the 6x32's fit the best. I don't think I rethreaded or stripped the holes in the drive trying the 6x32's because there was no shavings. I'll have to check the drive for markings. Though, now I'd be honestly surprised if it said M3 since I already tried those. M4's were too big.
Thanks for the tips on the DVD, too.