Just a post to state I have added the picture behind the main heading. This photo is of Pauls AE wagon and an Australian $2 coin taken by Darren Hodges (B67).
I have been thinking of possibilities of scratchbuilding railmotors utilising the method Paul uses to make his wagons. The Victorian Railways DERM (Diesel Electric Rail Motor) seems like the most obvious choice as it is very similar to the AE car and would require minimal modification to the design.
Still at the thinking stage at the moment. I guess ill have to work out the measurements of the mech and see if it will fit keeping to the scale measurements of the DERM.
For further reading and pictures regarding the DERM see this excellent resource: