OK, Today we fitted the front bearings/plates etc to one side...
I ordered some 8mm thick Aluminium plate, and drilled some holes! Then I fitted two SF20 self aligning bearings, a short 20mm shaft, along with some spacers. All with 12mm bolts! Way over engineered!
 

Onto this I fitted the sprocket (19teeth / 3/8th chain) that transfers drive from the rear wheels/motor to the front. Now we have all four wheels driven.

Now stood on the front end after I tidied up! The side plate that has the bearings bolted into it was drilled and tapped in position with the chain very tight. It will wear in and develop a little slack eventually, but the whole plate can be loosened and slid forwards if required.

A view from the inside showing the pair of SF20 bearings and spacers... This block of 4 spacers, two bearings, and an aluminium plate took all afternoon! Looks good and strong though.

Trailer wheel, now fitted on to a turned down, and drilled and tapped ex v-belt pulley using a "taperlock" shaft fitting, because keyways are useless for reversing torque loadings...  Ask any of those people who have all that clunking on a powerchair. They wear and fret!  Why they don't do it like this is beyond me!

A view of the modified pulley wheel, and spacers, and taperlock fitting from the inside!

From the back!  Imagine this (finished) with a black leather Recaro seat, arm rests etc.