I don't see why it couldn't be done.
But you may just want to get a Thruxton, it would be a bit cheaper- though it may break your old lady's heart...
If you went through all the work to do it, you might as well upgrade everything, as far as the suspension goes. Y'know?
I have an older and somewhat cafe'd BSA Victor. I haven't lowered it or changed the front end much- I think it turned out pretty good for a scrambler type of bike. It still has the small front headlight, dual seat, and mid sets, so it's not totally cafe'd yet- but it looks pretty cool (to me anyway).
Your bike would look pretty similar in a way. MUCH bigger and faster though.