The 2.5" or 3" would have walnut RB Magna stocks, and the longer ones Target stocks with the bigger (extractor) cutout. Call it about $25 for the former and $40 for the latter. Hope this is helpful.
Ditto what is said above. If this is a passed around gun check the grips out to see if they have anything on the underside of them. Sometimes that has the answer... Target stocks especially are very copied but usually a replacement grip has the mfg info on it.
Purchased the gun over the weekend. I took off the grips and Sept 91 is written on the inside. Ser. no BHL****. I tried to post pic but can't figure out how to do it!