Ruston works. It seems that the rods I made up aren't all required for the model. Apparently some prototypes didn't have the jackshaft drive so two different sets are provided. I had been wondering how to fit both of them !
Anyway, the jackshaft is made up from laminations and attaches to the Slaters square ended axle. I would like a bit more thickness - a couple more laminations should do it. That would get the retaining screw below the level of the crank face and stop the wobble.
Apart from this, it's all pretty easy. The holes in the rods are about 1mm larger than necessary but don't seem to affect anything. Long crankpins are needed on the crank and rear set of wheels. I only had one set so improvised by glueing the retaining nut on the pin otherwise it unscrewed after a few revolutions.
Pretty quickly I had a chassis that worked. It has run a few miles held in mid air on a couple of flux tubs with nothing jamming or falling off. With a jackshaft drive this is pretty good as I've encountered some horrors in the past.