There is an interesting chapter in "War Birds" by Elliot White Springs
where John Grider (the Unknown Aviator of the book's sub-title} has his mechanics revamp his cockpit in his SE-5a. He tells of replacing the stick with the stick from a Camel, from which he can fire both guns via a bowden cable setup. Some levers looked like an old fashioned emergency brake handle and others activated the bowden cable (like a choke cable) through a simple rotating lever like the ones shown in Blue Max.
I dunno about the DR-I. I never landed on that side of the lines.