Bob, I had one. Back focus is 1.60 inches, the lens can't be put in shutter, and it is too fat to pass through a 2x3 Pacemaker Speed Graphic lens throat. And it covers 6x6. The only way I could see to use it was on a 4x5 speed Graphic. Shooting 6x6 on a 4x5 Speed seems a little silly.
The OP's example was removed from a Maurer aerial camera, most likely a KE-28.
I didn't call the Elcan sucker bait, that's the 300/5.6 S-Tessar.
A Lens Collectors Vade Mecum has Tessar-S 300mm f5.5 as an aerial survey lens for the U.S. market.
S Tessar in shorter focal length as Micro Copy lens.
Elcan f2.8 150mm This was an aerial lens but no details are available. One report says No138-
154x with linear iris scale in bronze finish to f22 on 8-blade iris in anodized alloy mount.
ELCAN=E.Leitz, Canada, at Midland Canada