AXM Paper Space Scale Models

Probably 163 gsm.

> There seem to be two kinds of 90 lb cardstock - cover and index, which are completely different weights.

I would assume index would be the default, if unspecified. That's at the lighter end of the scale for index cards and the like, and a good weight for most paper modelmaking.

90 lb cover might actually be too heavy to go through some desktop printers without problems.