54 minutes ago, Fred W. Hargis Jr said:

across the depth of the top (I'm guessing it's 2-2.5" or less) wood movement differences between species isn't going to amount to anything. A bigger problem may be getting the finish of the top's edges to glue on additional pieces. You'' have to get to bare wood

Yes, I think thickness is 1.5 inches, and it's unfinished. So likely doable. Also thinking about how to attach that to the cabinet boxes - oversized holes with washers as figure 8 fasteners aren't possible?

Also, as an alternative, debating on using some of the 1/2 inch plywood I have, and glue up to allow 1 inch thickness with a space for the t-track. Then I could use the butcherblock for a workbench surface, adding some doghouse and vises (future project)

Figuring out some of this as I go...and hopefully get on a right course of action. Likely watched a few too many YouTube for ideas!! 😬

Consider not fastening them at all. What you could do is screws cleats to the bottom of the countertop that fit snugly inside of the cabinet. The cleats prevent side to side movement, and the weight of the topps plus whatever is on them hold them down. My workbench, assembly table and router table are all done this way.

1 hour ago, Fred W. Hargis Jr said:

screws cleats to the bottom of the countertop that fit snugly inside of the cabinet.

I like that idea but the cabinets already have tops. I made the boxes will full backs and tops. I didn't want to just use stretchers as I have had "mouse issues" in the past so wanted to make the cabinets more enclosed. So I need to secure the counter to the tops in some way.

Then I would probably just run a few screws up from the top of the cabinets into the countertop material....just putting some in the center of the assembly, it won't take much, maybe 2-3 screws in each cabinet box.