Jack, I think that I have the same carb as you...Rochester Model B manual choke...on my '57 with a 235. I had the same issue with sediment and discovered that it was rust in my gas tank getting past the fuel filter. I had to end up replacing my gas tank.
I rebuilt my carb a couple years ago with a kit from Mike's (
www.carburetor-parts.com) that has parts that are ethanol compatible.
I always buy ethanol mix and have not had any problems since I replaced the gas tank and rebuilt the carb.
Matt
