Not quite Steve
By 'compatibility' I was meaning that it is not possible to swap in a coupler assembly from another Bachmann loco.
The 45 tonner mounting plate is totally different from other Bachmann locos. It is similar in concept to the Accucraft AP-11730 coupling but even shorter in body.
It has no rear portion and only the front part that bolts to the pilot beam.
The coupler itself is a metal short shanked variety with a small centring spring also totally unlike any other Bachmann coupler (I have tons of different types covering all Bachmann variants to compare)
Anyheww.....
Mick was kind enough to send me and new coupler so that requirement was solved but I still would like to find the two steps before having to build them myself.
As they are pretty vulnerable at the front they would best be built from soldered brass strip.