Bill,
If you can't find what you want, I have a 30" full choke vent rib (not step rib but smooth top) that you can have modified to what you really want. I want
$175 shipped to you. The barrel is 0.725" bore, 0.690 choke for 0.035" constriction.
If you aren't interested, anyone else is welcome to respond to my message.
Thanks
Larry