What's all this? Are you keeping secrets from me?
1/8th or 1/4 mile?
If it's 1/8th mile I don't think the vehicle speeds will put you in a range where you need a lot of protection. I also think you will find these smaller local tracks (like Lapeer "International" Dragway) are much more liberal with their safety inspections than their major counterparts.
(Actual Audio: "....Zat yer helmet?" Yep. "You got shoe polish?" Yep. "Yer good to go.")
In either case I don't think that counts as a firewall change. The firewall change is intended for full tube frame cars where the original body sheetmetal is fitted over the rolling chassis/roll cage structure, with the original firewall being completely removed. Also - for cars with removeable trans tunnels (for transmission maintence and removal) it drives an additional crosscar bar below the dash in the roll cage.
Almost everything I do is through NHRA, but they have dedicated inspectors by region that you can consult. If there is a name in the IHRA rulebook it would be prudent to run your plans past him before you get too far.
K