Alternator on way out?

[Betti Ann & Preston Smith <prsmith@ns.sympatico.ca>]

1980 MGB LE

The ignition light has a faint glow.  After tightening the belt it is 
still there at times (not as often) and the alternator has a high 
pitched whine.

I assume the whine is attributed to the bearings going - does the faint 
ignition light suggest I should be looking for a rebuilt alternator?

How can I test the alternator's output?

If I need a rebuilt do I need a MGB alternator or can other units do the 
job with minimum fuss and bother?

Thanks
Preston