Hi Bob,
The CE-20A will work fine on AM but as previously posted the power output is fairly low so an amplifier will be very helpful.
Note that some varieties of the 6AG7 output tube do not like working in the horizontal position so be careful how you orient the chassis while doing alignment to avoid damage to the tubes. The position is only important while they are powered on.
If you haven't done so, download the 20A changes manual from the Bama website: (often the Edebris mirror site works better so also try:
http://bama.edebris.com/manuals/ce/20a/ ) and consider making any updates that your 20A does not have.
The main alignment procedure in the 20A manual calls for the use of a scope however most people will find that it is easier to do the alignment with a selective SSB receiver. The problem is that it is sometimes difficult to interpret the scope pattern if you end up with a mixture of hum, some distortion in the audio chain, poor carrier, and/or poor sideband suppression. Using an external receiver you can listen as you balance the carrier and adjust for best unwanted sideband suppression. I use a spectrum analyzer plug-in for my Tektronix scope so it makes setup pretty easy. It is possible to achieve very good suppression for one sideband at the expense of lowered suppression for the other. This is not really important if you are only using the CE for CW and AM but if you do decide to operate SSB with it and only plan to use it on 40/80 or 10-20 meters then you can optimize the adjustments for either LSB or USB.
The relays are becoming problematic in these units, many CE products use a "telephone type" relay with a high resistance coil that opens up over time. You can find replacement coils on the internet at very high price or if necessary you can still buy modern DC relays from Mouser and others that have a high resistance coil. This is definitely a better option than letting the exciter sit on a shelf for lack of a good relay so keep this in mind if your relay does go out.
Have fun with the CE-20A, it is a neat little transmitter/exciter. I have mine paired with an RME-4350 receiver along with the matching CE VFO and "sideband slicer".
73, Rodger WQ9E