This is just an observation BUT if your suit has NO SFI number you would need proof of what you are saying concerning the rating between SFI and FIA. I would bring the proof in writing from an accredited source. (I would not know one). You would need authorization from the chief inspector and a call to him would be a good start.
As for underwear if APPEARS yours would be legal by what the rulebook states.
Now the bad part, don't plan on going over 174.999. Remember the first paragragh states these specs are the minimum. I wear a 3.2A-20 on a class where the record is 168. Bonneville is not your typical racing venue where safety personel are within seconds. You need to protect yourself whatever speed you are planning with the best available...........Good Luck