nacho, you are a straight shooter and stand up guy, so don't be too hard on yourself. things in your neck of the woods are worlds apart from here in the states, so anything is possible. modifications to make something usable is understood to sometimes be the only viable option opposed to having something imported, which can/would be cost prohibitive.
don't worry! I can understand that and thanks
ok just called to the Swinger owner and explained me with detail how they did it!
as you say, is in fact a one piece assembly BUT they really CHANGED the hubs. Of course was a machine shop job. What they made is cut the hubs on both axles, cut splines on the Dart axle and press fit the B body hubs into the Dart axles. Then seam weld on both faces of the hub.
They told me is a pretty much tipical job done here for old BIG ton trucks ( several brands ) where original axles are become hard to find, so holds the heavy duty abuse with confidence.
They in fact race with this car and the job done for long time, although about a year ago or so, they got new aftermarket axles ( I think with green bearings )
so, it is posible to do it, but maybe easier modify the axle splines getting the right thickness axle on inner end ( per this website ) from B bodies if you want to keep somehow the stock assembly, not aftermarket pieces
http://www.hotrod.com/articles/mopp-9910-how-to-install-a-big-bolt-pattern/
