So, the vacuum breaker has a 1-1/4" chrome stem. The toilet has a 1-1/2" rear spud fitting. There was a 1-1/2" chrome ell with compression fittings between these two points. I can see that whoever did this used drain/waste pipes but it obviously was working fine for all these years.

I took it apart because it was leaking. (Leak started because the supply line coming out of the wall to the Flushometer is wobbly and every time someone flushes, the whole assembly moves. I am first going to fix the supply pipe so it doesn't move at all.) the old rubber washers between stem and ell and ell and spud were all brittle and cracked. I went to the local plumbing supply place to get some replacements (only nylon washers available.)

The guy at the plumbing place was shocked when he saw what I was dealing with (Flushometer in a residential bathroom!!!???) told me I was crazy to try and fix this and I should call a plumber.

Question: although this may be very unconventional, is there any hard in trying to get it back to the same setup that was there originally? Will compression fittings with nylon washers provide enough of a seal to hold back the pressure of the flush flow?

My other option is to just replace the whole toilet which I am quite capable of doing. Just need to make sure this old beast has at least a 10" clearance.

Thanks for the help guys!