Roud 303 Twa Knights lists:

Roud No. 303: The Twa Knights (7 Listings)

HOG'S HEART, THE
Source Thompson, Pioneer Songster (1958) pp.11-18   
Performer   
Place collected USA : New York   
Collector   

KNIGHT IN GREEN
Source Flanders & Olney, Ballads Migrant in New England pp.184-191   
Performer   
Place collected USA   
Collector   

KNIGHT IN GREEN, THE
Source Thompson, Pioneer Songster (1958) pp.18-22   
Performer   
Place collected USA : New York   
Collector   

These are US version but I thought they are versions of Buchan's Northern Lord and Cruel Jew, from Buchan's Gleanings of Scotch, English, and Irish scarce old Ballade Peterhead, 1825.

They are somewhat similar in plot, but I'm confused.

Richie