I'm in bimridder's camp with this- standardize everything. Whatever up front costs you go through to achieve this will be surpassed 100 fold by the saving via scheduling flexibility.
I do agree with Evo that if it's down and dirty, full time production on a manual that smaller frames are nicer.
I think eb's idea of the MHM pins dropping into slots should work well enough. It won't be dead on but probably really close and will standardize positioning of the art in any case. Or, just buy and possibly modify (if the MHM pin bumps the top block) a tri-lock platen. Reg on the FPU, tri-lock platen on the manual on press. So long as the film was originally attached in the same way, you should be able to mix/match systems.
I loved the old Rototex I used to have, it was my first press and it held reg better than anything I've used since. If yours is holding up well enough I might stick with it or invest in a few mods to make it easier to use. Mine had no micros though and I heard that the ones with were not so hot.
M&R's sidewinder, chameleon and Anatol's Thunder are the presses built to handle auto frames. You saw my experience with the purchase of a new Thunder, which I would not wish upon anyone, but the press does hold up our M3 frames now and is useable in a "normal" fashion. Just be sure to get one with the updates I instructed them to make, cross your fingers, burn some sage, say a few prayers....or just buy an M&R. The Chameleon really is like a manual sportsman, Evo's right about that. Great sampling press but that is not going to work for all sizes of people as a production machine in an 8/8 configuration. Don't plan on ever upgrading one to a second deck, the cost of a new second deck is more than a used 8/14 typically and I've only seen the upper deck being sold alone, used, once in lord knows how many years of scrolling through classifieds. Go with a 4/8 or a 6/8 might be perfect if they make it, an 8/8 is too much for some to spin day in/out. I personally enjoyed the extra chameleon workout, I'd rather feel like I was doing an ab workout all day than come home with the kind of kinks I get from being a desk jockey, but I'm a weirdo, and your staff may not share that opinion. Alan has a nice video on the Sidewinder which is supposed to be a lot lighter to spin.
Whatever you do, get side clamps with air clamps. Just suck it up and spend the dough for it, worth every penny and kinda necessary to actually use pre-reg to the best of it's ability.
If the MHM is the only press you've used in production then brace yourself to completely hate every other platen system out there. They all go out of parallel and need regular attention and re-adjusting.
Call me anytime if I can help.