Back in the day Pakosol, Kodak Print Flattening solution was used on all frerrotyped drum dryer prints. It definitely works, not sure how it effects the 200 year life span. Propylene glycol. I dry everything on a Pako, smaller, drum dryer, emulsion away from the drum against the belt, as long as you don't over dry. I've never used print flattening solution. The reverse curl of drying emulsion out definitely helps. To keep the prints from sticking to the canvas you need to harden the print. I use hardening fix.
Kodak made a print straightener, I have seen one, it steamed the print and ran it over a set of rollers in reverse curl. I suspect that this was a industrial tool. When you needed to shoot copy and the original would crack without the steam bath. Mostly single weight I suspect.