Did the conversion today and I took some pics as the original images are down.
Required parts.
What the drive looks like - note this one *came out* of the gearbox (didn't know what was in there). I didn't get any pics but I used a combo of a (n eventually plastic coated) cutting wheel, carbide cutter and a carbide burr on the dremel. You can see remnants of the removed black gear in the bottom right of the image. Recommend you melt it off instead, it'll be a lot quicker and less worried about damaging the spline on the shaft but messier.
What I didn't get was a picture of the flat I cut into the splined shaft. Cut 12mm down from the edge to match the new gear, or cut the flat from the gear. Either way works.
Note the gear shaft offset from the body. Also note the notch in the centre bottom, above thumb nail.
Note the difference in gear size. The shaft housing needs to be rotated 180 degrees to make room for the bigger gear. The body will spin in the gearbox but you'll need to cut a new slot for the retainer.
Original retainer location in relation to notch.
*NEW* retainer location in relation to notch which needs to be made. It's mirrored around the notch. Approx 3.5mm deep x 20mm tall and 4mm away from the edge (from memory).
Cut it with three hacksaw cuts. Could use a dremel or a square file instead.
I didn't neaten it up at all as I had already cut a tiny bit too far.
New gear on. I applied a bit of araldite to the flat area just to be safe. Don't use superglue as I think it may melt the gear. Notice I started cutting the flat out of the gear, before realising I could cut the shaft instead (and would provide better location on the shaft, not that I imagine there's much force on it anyway).
Note, the gear doesn't bottom out on the housing like the black gear. Top of gear is flush with the shaft (as shown in an earlier photo).
Going into the gearbox - if the gears are meshed, it should slide up to here with minimal effort. Note the location of the notch in the speedo drive body (should be pointing down).
All done!
