The older 35 amp alternators were pretty common, WAY back in the very late 60's and early 70's.
Since it's a Delco SI series alternator, most of the later SI series alternators will drop right in and hook right up to your current wiring.
The only thing I can't tell you is.... What your clocking is...
And it changed with the year and mount used...
Clocking is where the two wire plug in the side of the alternator is located.
If you look at the alternator from the back, there will be two mounting ears, one larger, on the bottom in the '6 O'clock' position,
One smaller, and threaded for an adjuster at the top in the '12 O'clock' position.
Most jeeps with an alternator on the passenger side of the engine are either 12 O'clock or 3 O'clock with the two wire plug.
I'm going to guess at 3 O'clock for yours,
Try having the parts guy look up a '1980 Buick Electra with a gas burning V-8 engine.
You will find alternators on that particular vehicle from:
42, 55, 63, 70, 76, 78, 80, 85 amp ratings, and one or two groove pulleys.
This link will give you an idea of what is available.
you don't have to use NAPA alternators, they are expensive for remanufactured, this page is just to show you there are MANY choices...
If your current alternator isn't clocked at 12 O'clock or 3 O'clock, poke around on that site changing the vehicle make and model and it will give you more options, (just stick with GM vehicles)
It's not the hard to change the clocking of an alternator, but there IS A TRICK TO IT!
So ask before you take one apart to change the clocking and I'll tell you how to do it.
Lots of the 'Mega' alternator rebuilders CLAIM 120 or 150 amps, but they are using stock cases and stock size rectifiers...
And the ability of the rectifier to cool it's self is what will be the determining factor in the output...
So, claims much over 75 or 80 amps is crap...
The alternator may be able to 'Flash' that high, but it can't cool it's rectifier, so it can't make that much amperage for more than a few seconds.
You are pretty much better off with a good Factory style remanufactured alternator than one of the 'Mega' versions that cost 10 times as much.
I run 65 to 75 amp version most of the time and I have GREAT success with them, even with dual batteries, large communications radio rig, and I winch & weld off the batteries, so it gets a good workout...
18 Gauge is plenty for the relay. Doesn't take much to pull in a relay.
That's why later model cars use them for nearly everything.
The actual alternator to battery charge carrying wires should be 10 Ga.!
If you need a big honkin' relay and socket, I might be able to help you out, let me look around and see what I have cluttering up my workbench...