For the record, here is the evap core info for the ones I used. I got the Factory Air units from Advanced Auto, and found that there are two styles of these. One was made in Canada, and the other in Venezuela. I used the Venezuela cores.
Fit 77-90 Caprice (all engines and styles)
Delco 15-6513
(Advanced Auto) Factory Air, 54432, $119
(Advanced Auto) Ready Air, 6259N, $155
(NAPA) NAPATEMP, TEM288046, $179
(NAPA) Genuine Air, 788046, $129