WOW! 2/0 for tube flys.
The hook config. that (for most of us anyway) use for tube flys is a short shank, ring eye type hook for tubes.
Other posts have also suggested a 'circle hook' such as the Mustad c71s ss which appears to have a relatively short ring eye shank. These do come as large as 3/0's. The "Owner" brand also shows a more triditional short shank "AKI" in 1/0-4/0 that appear to fit your needs.