Among my huge collection of parts, I have examples of both 240 and 740 seats, removed from the car. I made a fairly close examinatuion of both, side by side, and it looks like it might actually be possible, without too much difficulty, to mount the 740 seats to the 240 tracks. It would require some careful thinking and spacers of some sort, to make up the difference in width of the two seat tracks. In the process, you would lose the height adjuster mechanism, as that works in exactly the opposite way on the two seats (On one, the latch pins and mechanism are mounted to the seat track, and the holes the pins go into are on the base of the seat itself, and the other is the other way---without going and looking, I can't remember which is which) However, that would be a small price to pay for being able to use the sturdier, comfier, more readily available 740/940 seats in a 240, and, it looks like there is some range of possibility of mounting height, so you could decide beforehand on how high you want the seat, then mount it permanently at that height. You would also have to fabricate trim pieces to cover up where the seat belt reels used to be.

If I ever get around to it, (WAY too many projects going on at the moment) I plan to try it