Pulled this from a 1990 Dodge 1/2 ton ext cab long box, 360/518 combo. Is this a 120 amp alternator and is it a good candidate for a swap onto my 67 Coronet? It has a v groove pulley on it

You need to upgrade the charging system if you choose to put something like that into a 67.

The output will need to go directly to the battery , eliminate the ammeter ... but you know that

Yes for sure on the upgrade, I poked my nose into the other thread and saw the linked how to on bypassing the ammeter

http://www.ebay.com/itm/Alternator-Dodge-5234199-AL6510N-211-0121-121000-4040-/271464405164

Near the bottom

OEM(s):Denso, Chrysler
Voltage:12 Volts

Amps:120 Amps

Polarity:Negative
Output Stud Dimensions:M6-1.0
Reg. Location:External
Fan Location:Internal
Approximate Weight:14.28 lbs / 6.49 kg

Try mocking it up in place. The higher amperage alternators are thicker then the stock Chrysler units. I tried mocking up a couple on my 360. One was a 110 amp from a Toyota. The other one was off of a Dodge van I think. The Toyota piece was really close to hitting the cylinder head but might have worked. The van part did hit the cylinder head. It had one or two extra studded brackets that stuck out the back side. They would have had to be cut off in order to fit. I ended up going with a lower amperage alt so the case wasn't so thick.

As mentioned these are pretty thick and may touch the cylinder head.
The pivot holes are also larger, a 7/16" bolt worked on mine, but I relocated the mounting location on my "B" block up between the valve covers about where an A/C unit would have been. This fixed the issue with the depth of the alternator and also increased the amount of contact the belt has on the pulley.

That's the same as the one I had on my 65 Belvedere. I trimmed the studs to fit.

If the alt pulley does end up more forward you can space the crank/pump pulleys forward to match to take care of the belt alignment. speedway and 440source have flat shims. EDIT & check fan to rad clearance