I installed a long cage on the typical vintage Campagnolo Nouvo Record derailleur, in essence creating a Rally derailleur. I think the cage is aftermarket, but maybe it's Campy. It was in a "someday" drawer.
Theoretically the NR derailleur will only handle a 26 or 28 tooth cog. 'Pooh', I say. If you shorten the chain a little it will swing the jockey wheel down to clear the cog, and by moving the axle to the rear you can get to 30 or 32 teeth. Of course the shortened chain precludes a large ring/big cog situation, but maybe you shouldn't be doing that anyway. All this works on a stand; next Spring on the road we'll see if I can handle that big cog.
Now the crankset. This started out as your basic NR Campagnolo crank. It has a conventional 49T big ring, a Red Clover 42T triplizer ring and a 34T granny ring. I do have a 30T, but I have some doubts about clean shifting with the vintage front derailleur I am going to use. (The BB is a Velo Orange with a front spacer to kick it out to clear the granny.