Thought I'd throw some pics of this up in case anyone else needs the info. It's probably the same process in a crazy taxi / jumbo safari etc.
You'll need a spanner or socket set, philips head screwdriver, allen keys and a new drive belt. For 18 wheeler that was 187L 075.
First undo the three bolts to allow the cp to open.
Then undo the chain which stops it opening too far
This plate needs to come off. It's attached with four allen bolts
You then need to lever off this C ringwhich holds the axle in place.
These screws hold the potentiometer in place. You can loosen them and slide the little bracket to the side a few mm to disengage the teeth.
You can then just lift off the whole plate and slide on the drive belt. After that you just have to put it all back. The wheel will self center. You need to make sure it's lifted off the ground (I put a box under the cp front to keep it propped up) Then just make sure the pot is in it's central position when you reassemble.
I've got the cab partially built. Unfortunately the pedals are also in need or repairs. I thought they were going to be OK before I got it in hand. I also need to get a couple of minutes to look at the sound wiring since it's a bit different from a normal naomi. Not sure when I'll get this all finished since I'm too low on funds to pick up any new pieces til we get to August. I'll just have to get all I can done for free with elbow grease!