Cage/bar with modified frame - in SLOW truck?

[D13]

Done a lot of reading of rulebooks and online and really haven't found my answer.

I'm looking at relocating the frame of a square body truck,basically channeling the cab and moving the frame box further outboard - like just inside the rocker outboard. To stiffen the chassis I'm going to need some bracing, and it looks like I could run the roll bar right down the cab pillar. I like to run at the track occasionally, low 20's with my 130hp 250 inline. All the rules regarding cages and bars indicate nothing is needed until 13's or so. But they all stipulate unmodified floor and firewall which will defnitely not be the case. And as you guys have stated if you have it it's got to be legal even if it's not required. So am I going to have to put a full cage in this thing because of the frame, floor, and firewall modificatins?