Can't hurt to try it out but I would ask the seller to show you a pic of the pins. They might be completely different looking than the type of ECU's for Gen 1 Marks. I guess the worse thing that can happen is that it won't work or simply will not even plug in. Just like a 97-98 won't plug into a Gen 1 and even if, it wouldn't work. I have a W3Z3 from a 93 that I tried in a 94 that had a Z4H0 and the only thing that happened was when I turned the key on, the cooling fan came on and ran on high. The car would not start. It would just turn over and turn over but never crank up. I put the H0 back in and it cranked right up. The Z3 came out of the black 93 (with TC) me and my dad had here and it was running fine before he wrecked it. The inertia switch was triggered when he was hit. The car was t-boned on the passengers side and no damage to the drivers side at all. I still have the Z3 in the closet and haven't tried it in the 95 to see if it will work in that one. Been meaning to try it but just haven't messed with it yet. Really no reason to since the Z2 is working just fine. I have the DZA1 out in the garage or it's wrapped up and in the spare tire tub, just in case mine ever acts up for any reason.
The Mark VIII Geno has was built in 93 and has two ECU's and it might be possible that the catch code matches up. I really would like to know what Geno's catch code is for the SuperMark for both ECU's.