Yes, but I never thought they went so far as to put the instructions in a manual. By the time the A-26 came out I think that the enthusiasm for large caliber cannon had waned. It really was not very successful in the B-25 and P-39, and the 5 inch HAVAR was turning out to be far superior, although that is not what Rudel thought. The XA-41 had four 37MM guns but it never got past the prototype stage. Interestingly enough the A-26 manual refers to the right set next to the pilot as "the loader's seat." There was no copilot as such, although I talked to an enlisted Korean vet who said he rode there next to the pilot and they took turns flying the passes when firing the rockets. The pilot wanted to salvo them all on one pass, but oddly enough that never seemed to happen; must have been some problem with the firing switches.
Of course, the guns section I posted is just an excerpt from the complete A-26 Erection and Maintenance Manual I provided.