For the T-Tracks I just screwed them to the original waste board with some 1 1/4 inch drywall screws. I would have used shorter ones but those were handy. I just had to make sure that I didn’t screw into any of the extrusions under the waste board. I used the spindle with a bit to align the first one so it would be straight inline with the Y axis. Then after the first T-Track was screwed down I put in the first piece of MDF that would be the new waste board and used it to space the next Track. For the waste board pieces, I drill slightly oversized holes that would match the predrilled holes in the original waste board and then counter sunk the screws to hold them down.
For the Y axis, I did make new Y end plates and raised the axis about 1 inch higher. That made up for the additional thickness of 3/4 inch MDF plus gave me a little more height just for grins.
I made the new Y end plates from 1/4 inch thick 6061 aluminum. They are very sturdy. I had to get new screws to attach them but Lowes carried them. I also made the screw holes very slightly oversized to allow for adjustment of the Y axis height to insure that it was parallel to the waste board.
For hold down clamps, I made my own. Everything you can order online stand up way to high and can interfere with all sorts of stuff like a dust shoe, and even the carriage itself. Mine are low profile and work great.
Charley