Thanks for the input. I remember a name similar to the name "Sparta-matic" used for the cart machines. (Or, have I forgotten that, too?)
I've been checking the magazines on the American Radio History website and so far have come up empty.
Sparta-Matic cart machines were widely advertised. Check that site, but in the Broadcast Engineering Magazine search like this:http://www.americanradiohistory.com/Archive-Broadcast-Engineering/Broadcast-Engineering-IDX/search.cgi?zoom_sort=0&zoom_xml=0&zoom_query=sparta-matic+tape&zoom_cat[
Also, the site will have about 20 issues of Broadcast Programming & Production available in a few days, and there are numerous ads for the Sparta cart machines there.
There is also a Sparta Century cart machine on eBay right now at http://www.ebay.com/itm/SPARTA-CENTURY-SERIES-4610-TAPE-DRIVE-CART-/280803322657?pt=LH_DefaultDomain_0&hash=item41612eab21