The barrel OD is too small to properly put chokes in it for steel, it needs to be at least .825" for a steel safe choke to be installed. My 1926 A5 has a solid rib and Full Choke, with #7 lead it patterns really well, so I would say Bismuth or Classic doubles would work just fine. The problem is, a seasons worth of shells will pay for a new barrel.

Best bet is find a fixed choked Mod barrel, Belgium or Japan, and shoot the snot out of #3's or #4's. I know a person who shoots an 66 A5 mag with a Belgium Mod barrel and reports not one scar.

I found an Invector + barrel NIB for $250 for my '26 Standard A5, they are around, you just have to hunt for them. I have a 66 Light 20 with a Belgium Mod and Japan Mod barrel with Tru-chokes installed, and I just bought a Invector + barrel for it.