[Graham]

The motor will be glued in but an adaptor is easy to source, my question was can you put ballast in that space instead?

I think that the intended way of fitting the motor into the chassis must be upheld. So the original Ninco motor adaptor or a replica ensuring that the motor assembly is fitted into both the forward and rear chassis lugs must be used. If this provides an opportunity to fit the ballast around the adaptor but still within the chassis, then that would be ok.