TriBSA

This what is top on the list a TriBSA.
You slam a Triumph 500, or 650
into a BSA B50 frame
most use BSA 4 speed gearboxes
which maybe a little on the small side for a 650
then you polish it off with Norton Roadholder forks.
The tanks Ive seen look like run of the mill Triton tanks, and will probably be the easiest major part to find.
This bike really speaks to me, mostly because you don't see them on this side of the pond.
Now I've got to figure out how to rebuild the engine in the living room without the landlord freaking.
That and I think my wife needs that catsuit from the first picture, rowr...