|Looks like I really need a dremel. Those things look like I would've loved using them before.
Say, Beer Hunter, isn't that frame of yours kinda hanging loose in that setup? If it would be tight it would limit your trucks. I wouldn't dare to grind with a loose frame.
Love the idea of your setup though. Crossbreeding is fun.
For my own problem, I have an idea. Why not fill(like biff said) and surround the frame with plates of wood or other material, drill some holes horizontally and put in some of those pipe-screw things we use for inline skates. I'll make a drawing.