Innocent question alert... Why isn't the lip on your high lip trackball even with the finished plexi surface? Just my opinion, but I don't see the point to recessing it. It seems to be causing you more trouble than it's worth unless I am missing something. I am also wondering how you are going to get that bevel to be accurate and look good. That's a very tough cut to make...
Also, I question why so many people here bend over backwards to get 5/8" board for their cp. What I am doing for my cp (with a high lip tb no less) is using the same 3/4" I used for the rest of the cab. My t-mold slot is dead center in the board and with 1" tmold it will line up perfectly on the top once my 1/8" plexi is on there. The bottom will have a 1/8" overhang which can be easy trimmed once installed or simply left (I haven't decided yet).
It seems people around here are afraid of trimming tmold. In all actuality, if you talk to a professional cabinet maker, they will tell you that to 'properly' install tmolding you need to get it slightly over sized and trim both sides of it with a chisel once installed. It's so easy to do and makes the surface of the board line up PERFECTLY with the edge of the tmold. Very professional looking. Other than my cp, I used 13/16" tmold on 3/4" board which turned out perfectly once trimmed, even when my slot wasn't perfectly centered.
Just some ideas for you. Take them for what they are worth...