If wiredgeorge didn't figure it out, then there probably isn't a simple solution. He's been doing carb work for years. still does.
The 79 airbox ducts are longer than the 81-on ducts and the airbox holes are probably different diameters. From the diagrams at partzilla the frames, airboxes & battery case stuff are different, so the airboxes probably don't swap >> even if they did, there's still the problem of the distance between the airbox & carbs which I would assume is greater on the 79 because of the longer ducts. On some models when the stock ducts are NLA, some guys have no choice but fab ducts from radiator hose or rubber plumbing fittings or something, so this may be your only solution to keep the airbox.
...
