New to me '39 B

Hi everyone, My wife surprised me with a new tractor. Right off the bat I have some questions, I tried searching the forum for some insight into them but did not have any luck.
I believe It's a 1939 model B from the serial number. I think it needs a carburetor, I'm guessing those arent cheap or easy to find because the one that is on it has been brazed. Any insight on where I could find a replacement would be appreciated.
My reason for this diagnosis is it will start but sometimes backfires before it does, it will rev up but has almost no power. It has a 60" yanmar/cub cadet deck under it and I never did get the deck fully spinning, killed the tractor twice trying. It will drive in ALL gears and does NOT pop out, when in 2nd or 3rd the speed varies as in the engine is struggling with the load.
The other problem is the throttle linkage does not work correctly. It will throttle down but the lever wont make it throttle up, I have to get off and move the linkage by the carb manually. Wont lie havemt spent much time on this....I was till the engine fan tried to remove my finger(I'm fine, Pride hurt the most). I'm thinking I'm missing a spring. Thanks in advance, I might upload some more pictures if I can get it figured out.

front wheel / rims look like a 39... but has several "up grades"  like the dish seat, alternator, distributor... and maybe the starter..

Thank you for the info. Guessing im going to have to f8nd a used carb somewhere and have it rebuilt or rebuild it myself. As far as the "year" and upgrades the SN is B23207, which shows mid to late '39 according to Tractordata.com(yes I know not always accurate). It's possible it has a different transmission/rear end. It also have the foot brake kit in place of the original hand brakes(perhaps the reason for the seat?). I want one of those bigger bench style seat that has the backrest, I wonder if the brake linkages would clear, if not id imagine thats why it has this seat. 🤔