Here are the carb part numbers used on the gas 811's. You'll just have to figure out which one fits your application.
I Googled the part numbers, and new one's look to run from $255.00 to $280.00. I did see one on Yesterday's Tractors ads. A new one, and the guy will take $125.00 for it. But not sure how old the ad was.
I checked manifolds, and unless I missed something, they appear to be the same. The LP models do have the vaporizer though.
I found these part numbers on Ford/New Hollands parts site. Thought for sure they would be on Case/IH, but wasn't... Just for giggles went to F/NH and there it was. Just typed in 811 for the model #.
Hope this helps..!!
C0NN9510G CARBURETOR Carburetor Assy., 172", After S/N 126524, This Carburetor Assy. Does Not Use Ref. 2 thru P/N CAPN9590D Repair Kit, Start Year: 01/01/1960
1 1 B8NN9510A CARBURETOR Carburetor Assy., 134", This Carburetor Assy. Does Not Use Ref. 2 thru P/N CAPN9590D Repair Kit, Start Year: 01/01/1958
1 1 B8NN9510B CARBURETOR Carburetor Assy., 172", Before S/N 126525, This Carburetor Assy. Does Not Use Ref. 2 thru P/N CAPN9590D Repair Kit, When Using This Carburetor on Older Units, M