When I talked with the Crane's people they assured me that according to Cranes, there has never been anything other than 90lb cover. The Platinotype name was created after market. I have verified that on a few occasions.
This is correct. Platinotype is not a Crane designation. It is simply a smooth surface cover stock.
You might try one of the Neenah Paper Classic Crest Super Smooth Covers. I have no idea how it works for pt/pd however.