I am sorry I disagree. The GCR in the general section states:
All cars must be equipped with a safety fuel cell complying with these specifications, except for Showroom Stock, Touring, Spec Miata, and Improved Touring. All safety fuel cells shall be constructed and certified in accordance with the FIA FT-3 or higher (FT-3.5, FT-5, etc.) specifications. All safety fuel cells shall consist of a foam-filled fuel bladder enclosed in a metal container at minimum.

So according to this the specifications in this paragraph do not apply to IT.

And then in the IT section:
The stock fuel tank may be replaced with a fuel cell. The fuel cell shall be located within twelve (12) inches of the original fuel tank location. Additional reinforcement may be added to support the fuel cell, but such reinforcement shall not attach to the roll cage. Floor pan may be modified for installation.

I use a Jaz cell.