Has anyone compared the two butt plates (rectangular vs. triangular)? Do any of the screw holes and/or strap button hole matchup? I have the rectangular model B60. If I were to replace it with a B6 having the triangular end, what issues would I face? Finally, is the actual plate easily transferred from a B60 to a B6? I wouldn’t think so, as my B60 appears to be riveted.