The float and float needle *can* be removed from the 'dexter' carburetor without removing the carb.
To order new float needles, I needed the number on the seat. Now there are two on order:

http://www.mgcycle.com/index.php?mai...oducts_id=1335

Hopefully that'll solve my carb leaking problem. Oh, the floats are plastic, not brass. No gas in
them, so apparently they're not leaking.