[brian]

I just replaced mine last week. I got tired about worrying about having air pressure to flush the toilet.
I bought a flange for the floor that the toilet bolts to that required a 4" hole, I was able to drill the hole Offset from the original smaller hole to move it over about a 1".
That gave me enough room to mount the flange that bolts to the top of the tank, the flange on the tank   
Requires a 3" hole to be drilled in the tank, I was able to drill it straight down from the 4 " hole.
I drilled a 4" hole in a scrap piece of 3/4" plywood to use as a guide for the hole saw and screwed it to the floor where I wanted to drill the hole. Hopefully that will give you enough room.
It worked on mine. You call p.m. For my phone # if you want to talk about it.
We went camping at choke canyon lake last weekend and I am loving my new toilet. Paul

Hotrodhornet:

So you enlarged the existing hole in your waste tank?