Here's a thought…
….how about a firebox door in one end at the bottom.
….a baffle plate above that…
...and a grate above that
...then cut about 4 inches off both ends of the lid you just removed and weld them back where they were.
….hinge what's left of the lid with a strap frame and some firerope to have a better seal
...install the chimney through the end wall at the top above the FB.
Voila! You've got a RF with the firebox underneath the Cook chamber - no need for the other barrel at all. Might even work better considering how thin the metal is on those barrels.
FWIW