I shall be grateful if you could help me wi
There were two different types of floats used in the B carbs. If you are using the barrell shaped float, the bracket going from the hinge to the float should be parallel to the gasket surface of the top casting. If you are using the other style float that is more flat and oblong, you set it so the solder line of the two float halves is parallel to the gasket surface of the top casting.
The main jet is not the same on an A carb as the B.
If you are rebuilding the B carb, I would recommend you get a copy of the new book by Rex Reheis. It is part number BC-1A and gives a lot of good detail on rebuilding the carburetor properly.