By my book that I have on gun values the difference from 67 and 68 was in the sights the 68 was fitted with a factory scope and the 67 was a upgrade of the 60, 67 were not serial numbered for domestic sales but were for foreign sales the 67 list as follows for sporting rifle and not the smoot bore exc-300 vg-250 fair-125 poor 77, the 68 list without factory scope list for the same as 67 except fair is 100. Now if you have the one with factory installed scope then the price jumps exc 750 vg 500 good 300 fair 200 poor 150.
This info is taken from the 2010 standard firearms referance guide.
This will give you some idea as to the value but always remember that true value is what a collector is willing to pay and a lot of these books use auction house prices which may or maynot reflect what you can get in your area. the 68 was dropped in 1946 with sales at about 101.000 the 67 was dropped in 1963 with sales about 384.000
But at least you have some Idea of value and I hope this info is of some help
Deaconllb