I converted a GM vehicle from the original external-regulator style alternator to the common internal-regulator alternator. Found a couple of alternator conversion tips on the internet; one of them is hosted RIGHT HERE at Chevelle Tech in the Tech Reference section.

http://www.chevelles.com/techref/ftecref14.html

and also

http://www.hotrod.com/techarticles/marlan_davis_technical_advise/photo_22.html

After about 50 miles, smoke billowed out of the alternator like it was on fire.

I went back into the wiring using GM (Delco) service manual wiring diagrams; and found that both of the above sources have a mistake. They have crossed at least one wire between the external regulator connector and the alternator, then compensated for the first wire error by re-arranging the jumper wires at the regulator connector. Both links above are connecting the wire from the terminal marked "F" on the external regulator connector to the terminal marked "1" on the alternator. That is incorrect. It would be better to connect the wire from the external regulator connector "2" to the terminal marked "1" on the alternator. This preserves the original color code. The terminal marked "F" on the external regulator connector should go to the terminal marked "2" on the alternator. Again, this preserves the original color code. Some alternators have both the number and a letter identifying the alternator connections. 1 = I; 2 = F; where I represents the Indicator light terminal and F represents the Field terminal. Therefore, F goes to F, which means "2" at the external connector goes to "1" at the alternator.

By crossing those two wires, the jumpers as shown in the diagrams in the links above are correct, and the system will work even though the color codes are wrong. My mistake was to use that jumper arrangement while preserving the "correct" color code arrangement at the alternator.

I created a better graphic that shows correct color codes to the alternator, a revised jumper wire arrangement at the external regulator connector; and preserves the remote voltage sensing that can be of benefit to our older vehicles that have undersized wiring harnesses.

http://www.chevelles.com/showroom/data/500/medium/Alternator_wiring_harness_conversion.GIF

it doesn't matter which wire you use from the alternator- either the blue or white wire from the stock alternator plug can be taken out of the stock square plug with a small screwdriver and snapped directly into the flat plug for the new alternator. at the regulator side, you can make a jumper to tie whichever wire (blue or white) you used on the alternator side to the brown wire that goes to the dash.
i have always used the blue wire, and totally removed the white wire out of the harness to clean things up and prevent problems down the road.
i also just loop the big red wire on the alternator plug right back to the big terminal and run a big cable from there directly to the battery just like GM started doing in the 80's.
i've done this on 5 or 6 of my own personal vehicles, and on a number of friend's cars and have never had or heard of a problem related to my wiring job. i also just did it on a 47 Chev grain truck a couple of weeks ago. i still need to get some wire and 12 volt lights and rewire it since the mice ate most of the wiring it, but it charges the battery at 14 volts while running.
i've even put a few Chev alternators in Fords without a problem.

Is there a way to tie this into converting a single wire, aftermarket alternator to a 3 wire using the 2 extra posts that are hidden under a cap as most are?

it doesn't matter which wire you use from the alternator- either the blue or white wire from the stock alternator plug can be taken out of the stock square plug with a small screwdriver and snapped directly into the flat plug for the new alternator. at the regulator side, you can make a jumper to tie whichever wire (blue or white) you used on the alternator side to the brown wire that goes to the dash.
i have always used the blue wire, I agree, and I have always used the blue wire also. As long as the brown ends up at terminal 1 at alternator.

Is there a way to tie this into converting a single wire, aftermarket alternator to a 3 wire using the 2 extra posts that are hidden under a cap as most are?
I won't buy a "one wire" alternator; I believe in the benefits of using remote voltage sensing. So far as I know, the "one wire" alternators use a different regulator than the "three wire" regulators--but the difference may be just that the two regulator terminals are tied together.

If that's the case, it should be possible to split those two terminals electrically, use #1 to drive the alternator light, and use #2 for voltage sensing like any other regulator.