highball mounting plate has a larger hole because the ball itself sits higher, and comes through to a larger diameter point on the ball.
I have a highball with the mounting plate from happs, the plate is about 1/16" thick and has a lip of about 1/16". I recessed the mounting plate to be flush with the surface of the wood, tacked formica over the whole thing up to the lip which is convieniently the same thickness. very simple to do too.
if I understand what I've read correctly the highlip is an additional 1/8" higher than the standard, which would be convienient, bucause you could laminate over and conceal the plate, then add 1/8" plexi or lexan of your choice and it should come flush to the top of the lip.