Okay, thanks for the pictures! We can see what I was thinking was getting you nowhere!
I was on the wrondg side of the floor! And that does look like a tough place to get it moving.
Tell us what happens on trying to pull it out the side? Does it not want to move at all like it might be screwed or bolted down or does it move some but the lines are holding it from coming out more?
You know I'm shooting in the dark and never done this, so just throwing in ideas until somebody who may have done it might show up!!
But looking at the second picture from below, is there a plate on one spot that might give access to the plumbing on the heater back?
Looks like a terrible spot to get it off (if that is what I see) but maybe they did not give a good way to get there!
Looks like you have a big one going, so don't let me slow you down with talk!