I have purchased several new MVVS carbs for Magnum engines from 46 to 91 xls. Recently put one on a Mag 75 and receive performance similar to the 91.
Contact DarZeelon an RCU member who is the MVVS expert, he can set you up for much less than the stock carb. You may have to do some minor metal removal for a good fit but it's really worth it in the end. These are
good bar-stock quality that do not leak air and always shut down when you want it.