On the 68 it came with a low amp alternator with a external regulator. 

Hmmm...I'm having a brain fart right now....I know it can be done(and HAS been done).

Joel Take a look at this to verify it will match up to 68 I found this I will keep looking at it also 

This would be my updated as I read the 68 diagram Double check my work not sure of brown/wht wire, not sure if 68 has a gen light ? I think if their is no Gen light the Brown/Wht wire would be terminated at the regulator.

|UPDATED|7/13/2013 10:33:54 AM (AZT)|/UPDATED|

This looks pretty close to what I have except I have a black wire to the # 4 pin 

here is a kit might have info with it or contact vender

Here is a how-to for the conversion from an external regulator alternator to a "SI" internal regulator alternator.

The bracket configuration is the same for the external and internal alternators.

The colors of the wires called out are the "standard" colors and I can't swear that your car's wiring loom matches.

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When you convert from the external regulator alternator, you no longer need the regulator that is mounted on the radiator support or firewall.

Or,you could gut the inside of the regulator and solder a jumper from the F terminal to the 3 terminal inside the case.

Then do the same for the 2 other connectors internally. (2 and 4 terminals)

This would appear factory still with a cursory glance.

The diagram below shows the original connection at the old regulator.

The next diagram shows how you modify the loom at this location.

Unplug the connector from the regulator. Either make a jumper with spade terminals that plug into the harness terminals, or cut the wires and connect them together in the following way:

Notice that the Blue wire is jumpered to the Orange wire. The White wire and the Brown wire are jumpered together.

This next diagram shows what you have to do at the new alternator.

The white wire above, now should go to the new alternator terminal 1.

The Blue wire will go to the '2' terminal on the alternator.

You will need a new connector to fit the new alternator and they can be purchased at almost any auto parts shop.

In order to ensure good connections, I recommend that you always solder the connections and then use heat shrink tubing to seal it.

dang...pics are BIG! Need to modify this a widdle....sorry.

|UPDATED|7/15/2013 9:34:26 AM (AZT)|/UPDATED|

Hey Joel From the diagram I did above and yours I believe if their is no "Gen Lt" Their would be no connection to the Alt plug Term 1. I believe that provides Grnd for a Gen lt. Therefore the Wht or Wht/Brn wire from Term 4 of Regulator would be terminated(not used) it is 12vdc from Ign Sw in run and ACC. their would only be a wire in term 2 of plug at ALT. Term 2 is the volt sensing. does this seem correct to you?

Right, Bob..the brown wire would not be used with a GAUGE, only with an idjit light. I kinda went thru the diagram quickly at lunch, so I dint really have time to "finesse" it the way it should have been, but the basic concept is there. 

Now an alternator place in Richardson Texas said all I need was a 120 amp. alternator for my add ons.