Hey we think alike , I did it that way at least once to keep stock attachments which on some cars are reinforced . Others you can redrill with big washers under . Height of seat as upholstered a big part of that , especially on C D . Have done it so many times now I forget details of individual cars . Some had two bolt patterns too . Why I bring it up is it might impact longitudinal position of those pans under discussion . Bummer to go all through making that and seats too close
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Re that 2" further back mounting position you mention. I found I had the same legroom the problem, so a few years ago I came up with a pair of fabricated adapters that fit between the mounts and the seat frame. They move the seat back 2.25" and also give about an inch more tilt to the seat. It really transforms the comfort level. I made up several pairs for the taller guys in the club and they bought 'em up.
On a somewhat related vein, I never liked the very obtuse angle between my leg and the gas pedal, especially when it's floored - not even 50+ years ago. Matter of fact I can't even give full throttle for a quarter mile without getting a serious cramp in my calf. A light bulb appeared and I made up a gas-pedal-shaped block to stick onto my gas pedal. I tapered it from near zero at the bottom to almost an inch at the top. Presto. No more cramps, and it feels so much more comfortable under normal driving conditions too.