How much lack of similarity in airliner flying?

Suppose *both* pilots in, say, a B-737, were to die in flight
due to some incredible, but unfortunate coincidence. For
instance, one could die of a heart attack, and the other, say,
of an aneurysm. Now, I'll admit the chances of this happening are
remote, but it could happen; stranger things have.

So, suppose it did happen. If there happened to be an airline pilot
on board who was certified in any of the other Boeing models, from the
717 up the 747 and 777, but having no experience flying the 737, would he
have much of a problem landing the plane?

How about if the on board pilot had no Boeing experience, but only experience
with, say, Airbuses, or DC-9s, or the later MD-xx models?

I've been flying more recently, and these thoughts sometimes pop in my head
during those moments sitting up there at 33,000 ft. Also, people sometimes
sit around and babble about "the computer flies the plane" and such, and I'm
sure computers play a significant role with airliners now, but just how much?
I would think that humans still take the controls at least during takeoff
and landing, yes? And sometime I tune into the communications, and hear
that pilots are regularly requesting altitude changes and such. So, how
much does "the computer" fly the modern airliners now?

Also, would a highly intelligent, quick-learner, who keeps his cool under
pressure (but with absolutely no flying experience) have any chance at all
of landing the plane without killing everyone, while taking good instructions
from someone on the radio?

--
O.M.