I managed to fit up one side of the drive system in the ply mock up. I narrowed the chassis to 400mm but that maybe too narrow for the final build.
Never broke and shortened a chain before, so bought a good tool for the job which made the task a doddle. I cut slots out the back to move the wheel further back as advised by Mark.
The HDPE hubs I made worked well. Though the design of the wheel with 6 spokes one side (the side I fit the hub and sprocket) and 3 the other,limit the number of bolt options. I have one going through the sprocket, hub, and wheel clamping it all together. A second bolt locks just the sprocket to the hub. With the hub sitting over the 6 spokes there is no way this is moving. For final build I will glue it on.
Bolted the motors to the floor, and span it up.
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Vvvrrrrrmmmm
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The chain drive makes a different sound to a direct electric drive. Very satisfying.

No photo or video until I get it a bit tidier.

Second chain on order, some new bolts of optimal length, and various bits.
Weapon and self righter still to go.

Also have to decide if I get the aluminium floor professionally warer cut or attempt it myself.