An extra long 3/8" spade bit is inexpensive at a hardware store, some 3/8" grade 5 all-thread, the appropriate number of Stover lock nuts and some heavy washes work very well. A 6" or 8" spade bit will do it through just about any wood benchtop. Just back the bit out every couple of inches and clear the hole, slow down to a crawl as the bottom is neared because the bit will push large chunks out of the bottom if you aren't careful. The better solution is to stop as soon as the point goes through, go underneath and finish the hole with a regular 3/8" drill bit.
My LM is mounted that way; my turret press is lagged down into a green treated 4x4 bench top with 3-1/2"x3/8" lag bolts. How secure they stay, only time will tell.