When I processed 21/4 x31/4 film, I had a plastic adjustable roll film tank (Yankee) that handled 35mm and 120. I could set the reel at an intermediate setting and then push maybe 1/2 dozen pieces of film on to the reel and them develop as usual. Tray processing is doable, but there is a great danger of scratches handling wet film. Only if you are using orthochromic film can you develop under a red safelight. I doubt you can find that!!(posted 9254 days ago)There are 4x5 processing tubes on the market that should work for smaller cut film.
Perhaps the easiest thing to do is get a roll back and shoot 120 film.