The only real practical way to tie in your A pillar mount to the frame is going to involve trimming the cab support back. I realize you probably don't want to hear it since you went to a fair amount of work to put those in and they look nice but they are just plain flat in the way

. If you trim them right it'll still look good and make your life much simpler. The cage and under floor structure will more than make up for any loss of strength from cutting out part of the cab suport. I would also recommend that you trim the floor plates back to the other side of the pinch weld as their really isn't any advantage to having a large floor plate since you're mounting the cage to the frame and run little risk of pushing the floor plate through the floor. Or you could just drill new holes on the other side of the pinch weld.

I like what you are doing with the dash, I would have done the same thing if I would have known how much work integrating the dash into the cage was going to be.