Rear outlet, Floor mount, toilet replacement

I have back to back bathrooms, toilets are rear outlet and share same Y outlet, old toilets are 5 gal gravity feed, what can I replace these with? And will I have to change any of the plumbing? Prefer not to break up concrete to change to bottom outlet.. Any suggestions? thanks

There are not a lot of choices
Kohler, Gerber and American Standard make a rear outlet, floor mount with Flushmate pressure assist. Of those, I kind of like the Kohler, but they all work well.
Of the Flushmate tanks, either the 1.6 or the 1.1 gpf work fine.
I do not recommend the dual flush by WDI, EcoFlush. I quit selling that tank.

Installing

Hey, I have installed about 5 or 6 toilets with no problem. Are these any different in terms of ease of installation? Normal Floormount and flush ones are fairly easy that's why.

Thanks for the help!