SM2 or OSP for my Miata? Proper size of mag. decals?

[S Ahmad <aries_moon1974@yahoo.com>]

I have a turbo-charged '91 Miata and I need
classification help. Currently, I take my pass. seat
out to transport gear/tires for events as I don't have
a trailer nor Tire Tail and am not interested in
getting either at this point. Is this allowed for SM2
as long as I'm not below min weight? 

What size should I make the class and car numbers? 

Thanks!
Shaikh