Sorry Bruce, I disagree that all Twenty Twos were dual-fuel tractors. Tractors after 1J916 came from the factory as gas burners as standard equipment. I am using parts catalog from #8629 page 39. This page has two plates one for the manifolds used on tractors 2F964 to 2F9999 and 1J1 to 1J916, this is titled Manifolds - Tractor Fuel. 

The second plate is for tractors 1J917 to 1J5157, this plate is titled Manifolds - Gasoline.  

The carburetor part number. for 2F964 to 1J916 is 2B5738 and the carb for 1J917 up is 2B5678. Page 42 in the parts catalog lists 2B5738 as a tractor fuel carb 

and page 43 lists 2B5678 as a gasoline carb. 

The radiator curtain became optional at 1J917 "This group is also adaptable to Serial Nos. 1J917 to 1J5157". 

If 1J917 to 1J5157 were not gas tractors from the factory then there would have been no need for the 4B3027 "Fuel System Change Over Group-Gasoline to Tractor Fuel" that I pictured in one of my posts above.
Thanks
Ken

I have a nos one. I have not tried to unroll it in several years.
Ken