Good grief!  Anything GM will bolt in.  Buick, Olds, Pontiac and Chevy all
built cars on that frame, and they made a million of them.

Curious...  Unless he wants to talk about bolt patterns or something more
particular, I don't understand where he's coming from.  Maybe it's an issue
of price or availability.  Heck, there's a 350 in the same vein as the 305
and you'd probably be thrilled with it over the 350's you've dealt with over
the past 30.  Haha!  Seriously though, you should be able to get an '87 and
up engine that'll work and might even get the roller cam to boot.  Maybe
that's part of what he's addressing.
 Perhaps he's concerned about the heads, I don't know.  It just sounds like
he's being stupid:)  Granted, you might find a couple things different with
a newer block but it'll work just like you want. (ex. my '87+ 350 needed a
strange and pricey timing chain to use my LT-4 camshaft.  Go figure).
 Best of Luck (which is better than skill sometimes:),
 Drink