It's satin and laces up the front about 2/3 the way through 8 holes on each side with black lacing.
There is a ruffle across the top front, but it diminishes to nothing on the sides. There is boning on either side of the eyelets, then the boning channels become slanted. Again, I would use Ruth's Belasco corset for reference - it's probably the same. The bottom has ruffling all the way around, in addition to some black (tattered?) lace trim.
There are swags of red beads across the top front (be sure to secure each swag individually). The sequins are clustered more heavily around the center top and bottom, but continue to be dispersed over the rest of the corset.
Like the other's floorshow corsets, it probably closes up the back with hook & eyes, though a zipper would be better for quick-changing.
He has 4 red crinkled garter straps, and the satin on them seems to be similar to the trim used in the ruffles along the top and bottom.
My personal conspiracy theory? I think the Belasco corset could be the same corset from the film with minor modifications. It seems silly to me that after wearing it on set in December of 1974 Sue would make an identical one for the same actor to wear on Broadway 12 weeks later. Pay special attention to the beaded swag and boning channels. Identical. Besides, we already know Sue has recycled pieces from other productions (re: The Maids). Or is the film corset otherwise accounted for?