Check it by using it to measure the current of a lamp fed from the battery, a 60w lamp at 12v should show 5A.

Try these tests:-

1.  Short circuit the output of your rectifier and make sure the alternator is stiff to turn, you will only be able to turn it very slowly if it is working right.
2.  Connect your rectifier to the battery without your meter and try the same again. It will turn easily at low speed but when you exceed the battery voltage it should again become hard to turn. If this is so, then introduce your meter on dc current range and make sure it is equally hard to turn.

You could make a shunt for the analog meter by connecting about 2 ft or so of #14 wire across its terminals, you could then calibrate it with the battery and a 60w lamp or something that takes a known current and use that to check your alternator.

Don't do anything silly to the alternator until you have sorted this problem, when you know how it is performing is the time to think about changes.

If you give me all the alternator details I will try to do some calculations on its output.

You have 12 poles, 2 x1 x1/2  is that single or dual rotor?  9 coils 60 turns #14 wire.

Let me know the size of your discs,  the thickness, inside and outside dimension of one coil.