Bilenky put couplers in my old steel Mercian about 12 years ago. They do good work! I also had them re-braze my cantilever bosses as the old ones were wonky, they re-painted the frame & fork and I bought the case and packing materials from them. They do a lot of refits and your frame would be in safe hands. As for the economics of all of this, I suspect you won't save money unless you do a lot of travelling and perhaps even then, with all sorts of new luggage policies in effect, you'll never see the savings but it is a whole lot easier to get around with the smaller case particularly if your travelling involves buses, trains, etc in addition to planes.