Well I was corrected on what I have here, Thanks Chad.
Here you go. It is a NIB(never had an action in it) McMillian MKII Hunter for M77 MKII the mag box opening is 3.23" and it is approx 6.4" center to center on the guard screws. It is not marked short or long action so be sure to measure yours, i believe it is for a short action sporter barrel. By the way this is one of the most comfortable to shoulder stocks I have ever held.
$320 shipped Conus they are about $500 new. 3 day inspection if you buy it and it doesn't fit I will refund your money.