Alright, finally got my transmission in after a long time sitting, now the next thing to go was the alternator. Now my question is, should I continue to use my external voltage regulator type of alternator or switch to an alternator that has a built in VR one wire type. If change, what are the benefits. This is in a street rod.

In general, externally regulated and sensing alternators read voltage delivered to the harness and adjust voltage output. This compensates for any voltage drop in the charge wire.

"One wire" alternators sense voltage and adjust right at the alternator. While this is a lot simpler, it does not adjust for drops in the charge wire and may charge the battery slower. If the charge wire is short and heavy gauge it can work fine.

Whatever you do, suggest you avoid a reman of an old alternator. Quality has been pretty iffy. Powermaster and others sell new versions in externally regulated or one wire.

What alt do you have now & why are you thinking it might need to be replaced/upgraded? If you get a parts house alt I would suggest the 78 amper for an 89 M body (you'll recognize it by the thin stator in the middle seperating the two side cases). its a bit thinner so the front/rear spacing on the eng plus the adjuster bracket for the belt & possibly the belt also will need very slight modding but no big deal. Absolute best OE is the monster (Leece Neville?) with the fan vanes (like a water pump) behind the alt pulley but it is very heavy (it & the special brackets for it) but you may have alot of draws that need to be fed

I am very lucky that there is an alternator rebuilding shop a couple miles away so I always just have the old on rebuilt. See if you have someone in your area that does it.

I think it depends on a couple of things.
how easy will it be to replace it if something goes wrong.
by that I mean you are in podunk tooling around and it quits say on the power tour. how bad is getting a replacment.

How clean do you need the wiring to be in your engine compartment?

I care more about the first, though I don't actually drive that far, I also don't want to be out of a car for that long when it is down, that I have to order a power master whatever.

I keep the single field VR and run a dual field alt with one of the fields grounded.

gave me the most options on replacement with a standard LA front end.
however running a mag motor now, I don't have much choice in alt, but I still run the single field vr anyway.

I run a factory style 12SI delco for a 1985 Firebird 305. This is a great alternator and it's very easy to mod to fit.

You basically buy a universal chevy bracket and combine this with the stock lower one, just do a lap weld on them where they meet and can allow adjustment. Then you take the top bracket, flip it so it pushes away from the head instead of toward it, cut the bottom tab off, and add a additional spacing to the upper alternator bolt...and get a 4" length bolt.

Connections are also pretty easy.

What is the cost and availability of this Chivvy alt?

Depends on which version you want.
63 A is about $46.99 + $15 core (PN 7127-3)
78 A like mine is $71.99 +16 core (PN 7273-3)
94 A is $71.99 + $16 core (PN 7294-3)

The prices are all from advance. My local one had all three in stock, and if one died in the field you could use any of the 3 in a pinch. You can probably get them cheaper online. There are also some even higher amp versions, you just need a 12SI with 3-o clock clocking.

The plug for the regulator to connect to your wiring harness is $3.29. You'd then need a rectifier diode with the stripe on the alternator side in the "warning light" wire which will connect to any fused, 12V keyed power source and connect the other wire to the blue wire from your mopar alternator, this is the sense wire and will determine where in the harness it regulates the voltage to.

Been using this since 2011 without any issues. I even have EFI and Electric fans (Ford Contour) and it works well on all.