Jim;

Most questions you might have will be answered by going to the info page Rob posted (thanks for the referral)...Cons?...a Delco alt is not original, so I wonder if they'd let you into the "stock" class at the next show, I cant even think of any others...but quite a few Pros...double the output (and even at idle!), so a good stiff system voltage (you'll love the whiter headlights and might even be surprised to see the wipers running faster), and a fully charged battery is not a rarety, no more relay regulator, replacements are available anywhere in the US, and wont break the bank...etc. etc.

As Patrick posts, if it is a later (B20) block, which had a mounting boss in the casting and were delivered with Volvo OE alternators (Bosch, Motorola, or SEV Marschall), it would be an option to revert to one of those alts., but be prepared to plunk down a lot more bucks for an alt which didn't put out much more than the OE gen. (and you'll STILL have to change over to an external relay regulator...more bucks). It's (almost) as they say: a no-brainer!

Contact me off-line with specific question.
Cheers