OK, So it's a SG used by Saginaw Steering Gear Div, Saginaw, Michigan.
These are often found with extra letters and/or numbers stamped in the slingwell. We assume it's some code used by SG.
SG did use a Type III Low-wood Oval cut very late in production. Friend just told me (no books currently with me, I'm out of town) the Riesch book says at/after serial number 5,840,000.
If a real Low wood and not a cut down Hi-wood, I'd say fairly rare.
Even if Cut down.... with rebuild stamp and P proofs... they are sought after.
Any and all SG stocks that have the boxed SG and CC are pricey. Even more pricey if found with no rebuild or armory stampings, to include stamped P's on the front of the pistol grip. If in nice condition and marked RSG, just the Hand Guard can sometimes sell for $75.00.
Even SG Butt Plates are sought after.
Bottom line anything SG or S'G' pulls a premium.

My Advice spend $75 ASAP

HTH and Good Luck
Charlie-Painter777

PS: Look for Greenish colored ink stamped numbers inside the Op Slide Channel of the stock. You can look that up using our 'Search Milsurps' button to the upper right.