Thanks Guys.
Craig, do you have a 20320 or 5620T set by chance?
Rick,
No, I don't really have this as a "set". I do have examples of much of the mid-1950s stuff, including the components that would have made up the 5620T/20320, but I never purchased the items as a boxed set.
If this is the set you're looking for, maybe another forum member has one, or you could easily "piece together" a set by browsing a site like eBay. There are always tons of 283 locomotives for sale, and the cars are relatively common:
928 plastic New Haven lumber (not log) car
937 MKT box car with tuscan roof and ends
925 Gulf tank car - the 1956 version would have a die-cast frame, 1957 might be plastic frame
977 action caboose with rubber man (though some sets reportedly came with the plain 930)
A set like this just sold on eBay last week. They show up pretty regularly.
http://www.ebay.com/itm/AC-GIL...rksid=p2047675.l2557
It looks like that set had the earlier "metal man" version of the 977 (much easier to find), so that is probably also correct for a 5620T set.
If you are seriously looking for this set I'll keep my eyes open.
Craig