Ben, as far as I am aware Derek never built a frame for the unit construction motors. Nothing to say this one has not been altered to suit, but the frame up-tubes at the back of the motor cradle do not look long enough to accomodate a pre-unit motor.
There is a frame builder Essex way that could be the instigator. No idea of his name at the moment, but it may come to me after another glass or two.
On another note .... we too were thinking of going to Melborne (sp) at christmas. But I think the cost for myself, Corinna and the two kids would be prohibitive. Looks like the wifes sister will have to come back here if she wants to see us. Anyway, what the hell would I do for 3 weeks in the suburbs ? Apart from blagging a ride on something and going skydiving that is.