newbie needs help

[divecha]

Im trying to fix the rust in the floor of my 67 c 10. I bought the slip over cab mount repair pieces and the bottom ones dont seem to fit on the inside part wheres theres a triangular cut out. Can I just cut these to fit or maybe Im doing something wrong. Ive cut off the old rockers which also need replacing. If anyone has any pics of the bottom of their truck that they repaired that would also be helpful. Thanks to anyone who can help.