Just installed 4.7 IMS tank, now I can’t get the seat on

I got a used 4.7 tank the other day, and installed it. When trying to put the seat on, it’s unable to slide far enough forward to get the bolts in on the rear fender.

I’ve drilled out the tank mounting brackets to allow the tank to slide as far towards the front as possible, and it’s still at least 3/4 inch from lining up. Anyone had this issue before?

I have a tusk rear rack which makes it so I can’t just drill out the rear fender holes, since the seat would still be contacting the rack