Marks Hardware, 90 Series Mortise Lock
Model: 90 Series: primarily used on ornamental steel security storm doors.
Standard Faceplate Measures: 1 x 7-1/8;
Optional Faceplate measures 1-1/16 x 7-5/8
Old style had a smaller faceplate- can usually be removed and re-installed on new box

Backset: 2-1/2 inch - From faceplate to center of handle
Square Handle Spindle: 1/4 inch Square
The 1/4 square spindle is used with round knobs - Not levers (knobs: 301092)
There is a metal plate that prevents using a one piece spindle. This allows inside and outside handle to turn independent of each other and also enables the toggle on faceplate edge.

Handing: Left hand Reverse - Outswing door
Marks Locks are reversible, But better to order the correct handing.
See additional images to determine handing

Related Marks Hardware:
301067 - Used with knobs, model 90 lock case, Left hand Reverse
301068 - Used with knobs, model 90 lock case, Right hand Reverse
301069 - Used with levers, model 9000 lock case, Right hand Reverse
301070 - Used with levers, model 9000 lock case, Right hand Reverse

The Marks 90000 Series Levers used a 5/16 square spindle


Resource:
How to Rehand Marks Mortise Locks