Well dammit, looks like im abandoning some more parts i made lol. My dunham pneumatic closer showed up on ebay for about half price so I grabbed it up. Going straight to full automation. That means I have to let go of the direct coupling idea and go with the dual idler 5mgt setup. I guess in the end it's less wasted time and money. I can integrate all the pneumatics cleanly. The unit will have a single air line coming in that splits to 2 adjustable regulators, then a 4 way solenoid for the closer and a 2 way for the brake. Independent pressure adjusting for both. Back to cad I go. One thing I did realize is that I can just reassemble the original big belt design for turning any parts i need for the 5mgt setup with closer. It worked fine, just too much backlash for precision indexing, but it turn some parts no problem.
For the idlers I'm kind of wondering if it would be easiest to just use 2 big bearings stacked together. I'm thinking 40mm od, either 12 or 14mm wide double stacked for 24 or 28mm wide idler. No need for flanges since they will be right up close to the flanged 5mgt pulleys.