See
HERE for the bench seats in the front of a 90.
I have got RRC front seats in the front of my 110
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These are bolted in using the RRC runners, using the standard holes at the back, I had to drill new holes in the top of the seat box for the front bolts as the RRC runners are shorter than 110 ones. Then I had to reinforce the seat box to stop it flexing. Only problem to overcome is the lack of access to the battery box and the box under the drivers seat. I just moved the battery to a plastic battery box in the rear footwell and stopped using the drivers seat box for anything that wont fit between the seat box and the bottom of the seat..