My suggestion would be to pull an alternator yourself at a wrecking yard. Make sure to get the leads that will go to the starter relay and also the plug that goes in to the alternator. Cut the other wire far enough back from the alt to make a pigtail to wire it to the charge indicator wire.
When you remove the alternator from the donor car make sure to get the main charging lead and the plugs with with enough wire to splice for use on the older car's wiring. The pointer on the top labeled Plug just makes a loop to one of the terminals on the lower and larger plug. This should also be taken when you get the alt.
Pulley removal??? I just tried it and was unable to break the nut loose holding the old pulley or the one on the newer alt. I really didn't have much to work with. I would suspect the easiest way is to use a good impact and a very large set of channel locks or a vice to old the pulleys while breaking the nut with the impact. No doubt a puller of some type would be needed to pull the pulleys off of the shafts. Might even be easier to take both to a shop that works on Alts and have them do the swap!
Note that the old style alt has cooling fins behind the pulley where the newer one doesn't. The newer alt has cooling vanes inside at the back. I can't see where leaving them on the old pulley would make any difference other than maybe adding extra cooling?
See updated info below.
I saw your web page. Maybe this will help.
The pulleys are interchangeable, but you need to put a thin stainless washer behind a March pulley to make the spacing work. The shafts are the correct diameter. The washer makes up for removing the fan from the v-belt. The new alternators have internal fans that draw air through all those holes. An external fan would only block airflow. It's also nice not to have the fan there to scrape your knuckles!
If you look around the alternator case, you will find a slot, not a hole, but a slot. Look in the slot while you turn the armature and you will find a nice recess in the thick metal part of the armature that perfectly matches the slot. You can stick a big punch or screwdriver in the slot and that will hold the armature so you can wrench off the nut. This is the only correct way to do this, and the alternator is manufactures as such. Make sure you have found the slot and the beefy part of the armature, or you will damage both the armature and the case. Once the nut is off, you may need a puller to get the pulley off, but it shouldn't take much force.
You can also get a brand new pigtail for the internal regulator at Pep Boys.
Here's a picture of my '46 Ford with '72 351CLE and a '96 Mustang 135 amp alternator. Works perfect! I'ts not on the road yet, but I have started it and broken in the cam, and the alternator ran smooth and quiet and brought up the volts with very little heat.
--George at Devil Mountain Engineering