I managed to remove the bottom pulley and see that it has a spline and one of the 2 positioning bolts is located in the spline grove, so that along with the problems I would have in not being able to refix the circlip means my first idea is not practical. The shaft input (what the parts list calls it) as some play in it (from age) but still seems fit for purpose. I have noticed the gearbox is fixed to the plate using shims which raises the gearbox by about 12mm, so my next idea is to reduce the height of these shims which will make the bottom of the gearbox "shaft input" protrude further below the underside of the gearbox fixing plate. This will hopefully give my bottom pulley the clearance it needs so than it can spin freely and allow the drive to work.
