Year Manufactured?

I inherited a bolt-action shotgun today from my grandfather who passed away recently. My mom told me that the shotgun may or may not have also been his father's as well, but she doesn't remember. I was searching on the web for info on the year it might have been manufactured, but I've been unsuccessful thus far. I was just wondering if anyone here could shed some light for me. That way I could possibly estimate if this heirloom was in fact bought by my grandfather or my great grandfather. The barrel reads:
NEW HAVEN
Model 490 16 GA
2 3/4 CHAMBER 28 FULL CHOKE
MADE BY O.F. MOSSBERG & SONS,INC.
NORTH HAVEN,CONN., U.S.A.

I have not seen a serial number, and it has a 2 shell magazine.

 

MODELS 390, 390K-A, 390K-B, 490A
- 16 ga., 3 in. chamber, detachable box mag., mfg. 1971-76.
Grading 100% 98% 95% 90% 80% 70% 60%
$175 $150 $135 $110 $95 $85 $75