ours has a chain and not sure if any parts are still available
Interesting....
I have a Tucker factory manual that came with a 1980 Tucker.
On most of the Tucker pages (some pages of the manual are from component suppliers) there's a date. The page on the transfer case is dated "3-79" and the part numbers and photos sure make it look like Tucker used one transfer case for the 1300, 1500, 1600, 1700 and 2700 series machines.
But there are other pages that show what looks like the same transfer case dated "1-76"....
There is also a page on Chevron letterhead with lubrication recommendations. That has both Power Transfer Case (Chain Drive) and Power Transfer Case (Gear Drive) listings.
Evidently they made both (for a while anyway). My suspicion is the chain drive version was installed in lighter-duty applications.
I would recommend you call Joe Barron at Tucker. Darn nice guy. Tucker's number is 1-866 SNO CAT 1. You might give SnoTrans a call too. He may have a used transfer case available. I know a new transfer case (from Tucker) is
Big bucks.