Yeah, definitely replace those carriage bolts with your alternative. I did the same thing on a few swaps myself, always disliked those carriage bolts. Had to cut them off of a Nine Ball as they were so indented into the playfield the top nut wouldn't come loose and the bolt would just turn and chew up the wood.

I think there should be enough room underneath there for a six bank in that four bank spot.

Quicksilver is a great example of something being greater than just the sum of its parts. Not much in it really, it has about the same or lower coil count than similar games of that era. It just works really well with those great shots and ruleset. I operated one in a bar and grill for about six months and it would routinely outearn the Tron LE sitting next to it.