BBC mounts.. how the do these things fit on? or am i just that dumb?

[smoknbarrels]

I am sitting here looking at my BBC perches, I bought both left and rights from GM, and I am trying to put them onto my '67 which originally had a 6 cyl engine in it... but the problem is that they don't line up any logical way.? the only way i can see them fitting is if I put them on the two front holes and notched the frame..? I can't imagine this is correct? should I be cutting the frame rails?

can anyone confirm how these things should be put on?

thanks..