Whip -
There are actually 3 different riser shapes for the 1954 68" Kodiak II bows that I have documented. There may be others, who knows?
One is the same your 68" beefy riser, and other 68" is slightly different length and different limb profile. The other totally different 68" has a smaller thinner riser with lines like your slim 64". I actually have two of the smaller thinner riser 68". I'll try to add a photograph of some 68" Kodiak IIs to illustrate this text.
For the KII, there is both maple and walnut risers and lengths of 56", 60", 64" & 68 plus the prototype KII. In total I believe I have 11 different KIIs. As I say, it would not surprise me if there are others.