Hello Nigsbro,
I put a Cadillac 500 Big Block in a M1009 Blazer so I can help with your swap. It is not possible to just swap wiring harnesses unfortunately. The fuse block wiring on the inside is different too because there are provisions for the glow plug relay, different indicator lights, Gen 2 gauge, etc... The starter is also 24v and the batts are wired in series. I wired my batteries in parallel, disconnected the wiring harness from the diesel, pulled the diesel, put in the Caddy, taped up the Gen 2 harness, hooked the Gen 1 harness to the alternator, ran a keyed accessory wire from the fuse block to the choke and the HEI, and taped up the rest of the wiring. It worked great and just taping up the wiring allowed me to switch back to diesel after the Caddy blew up. If you are running a carb, the wiring will be easy. The old oil pressure warning wire plugged right into the gas sensor. All you need are electric choke wire, coil energizing or HEI wire, oil pressure, and alternator wiring. I used a mechanical temp gauge in place of the Gen 2 gauge. Any questions, let me know.<img src="emoticons/icon_smile_thumzup.gif" alt="Thumb Up"> Too bad you are across the pond or I would buy your 6.2L<img src="emoticons/icon_smile_smokin.gif" alt="Smokin'">