Changing body components on ANY two different numbered carburetors is asking for a headache, as well as an engine that doesn't run properly.
The term "flow test" is BADLY misused. A flow test is a test to determine the amount of CFM which a carburetor can flow. This is done on a "flow bench" using a non-volatile liquid (safety reasons). Generally, what a shop means for "flow test" is that they ran the carburetor on a test engine. With todays fuel, this will virtually guarantee the owner will have problems with the unit, as the modern fuel will evaporate, leaving a sticky residue. Of course, if the customer picks up the carb at the shop, and IMMEDIATELY installs it, not allowing the fuel to dry, the above does not apply.
Universal units which fit different size engines are calibrated richer than standard. I personally try to avoid these; or if I must use them, recalibrate them myself ON THE ENGINE.
Jon.
