A more precise date can be determined from the complete serial number.
Although it appears that the guns were generally assembled in numerical sequence, the shipments were not and some guns remained in inventory for weeks, months, or even years between assembly and shipment. The only valid way to determine the shipping date is by researching the individual serial number in the factory records. I have a first Olympic that shipped in 1976, 26 years after it was made.
Do not purchase aftermarket magazines unless you are determined to be disappointed with their peformance. Het originals from eBay or one oth the other on-line gun places. There is a Wayne Davis article about the after market magazines on my website at http://www.histandard.info/datapublic/Articles/
There is an additional file of enlarged photos from Wayne's article in the menu. The new High Standard in Houston is finallly offering a new magazine (their old ones were not soo hot) that has had several favorable reviews. These "good" magazines are marked with the letter "A" as shown in the Fred Valenti photos on the same menu.
Value, assuming it has an original magazine, would be in the $475 -$575 range according to the 2005 Blue Book and $470-$570 in teh 2006 Blue Book. If you have the optional weights or muzzle brake, these would add to the value as would the original box.