Norm-
While your description does not jive with the selection of Super Champion rims I have, Fiamme did indeed make a Pista specific rim, only seen them in the red label, but could well have been made in the other weights as well.
One way I would describe them is that the "sides" are not parallel to each other but if extended would converge within the diameter of the rim. About as close as an Aero vintage rim from the 70's or prior.
John Jorgensen
Torrance Ca USA