Dave LEib had themin his car for awile, but he is not on this message board. Here is a post from the MGBBS
"Will Munns, Cambridge, 1600 midget without front bumper - and P Reg F
There are two large bolts and one peg per rail.
The holes are on a slant, I bent these back horizintal with a vice.
I found washers which would fit around the fat part of the peg.
Then made up a paper template for drilling. (note LHS/RHS seat runners are different - more later).
(RHS) I drilled the holes for the inner rails so they went thru the chassis strengtheners as the previous seat, I added the washers and welded them into place over the hole for the peg, the thin part of the peg now pokes thru the floor and the fat part is bounded by washers. This process will leave the front mounting of the rail above the floor by about 1/8, add washers to suit.
I found that sliding the seat right forward, before fitting exposes the rear mounts, when these are in place you can slide the seat back to expose the front, and seat the seat. If you do this the other way around then even with the seat fully forward you cannot get at the rear mounts (crossmember gets in the way)
The LHS seat does not have the holes and the peg in line, the front mount is offset, I trimmed it back a bit to make them more in line to alow the peg and the nuts to fit within the original seat rail
I fitted the LHS seat in exactly the same way. BUT the tunnel is not symetrical so the LHS seat has 1" gap between the door and it, where as the handbrake binds, so when I next do this I will be moving the whole seat 1" to the outside, this should leave the nut in place in it's normal position and leave more space for the brake. "