so we have 18mm in the UK which is close to 3/4, Im going for 2x25 so 50mm for a very solid box. That will pull the PR forward even though Im going to flush mount it as is here and the amp will be further back slightly, all in all im guessing less of the PR and amp inside the enclosures equals slightly more volume, I just dont know if its that crucial to the operating parameters.I used 3/4" MDF. My PR is surface mounted, and I have used the same box. I believe he made the front panel thicker to accommodate the flush mounting and retain original spacings.
Heres my confusion on the front baffle. regardless of the difference between surface or flush mount, these 2 holes dont look like they are the same distance from the internal walls, yours looks like the the 4 extremes are cut right back to the walls and this one looks like its stepped in more.