I cant really say for sure but since you removed the trim, technically that would be a prepaired mod, IIRC. I barely have enough to attend events (havent attended the last two due to my tire being nearly bald and having to stretch the life), SO I havent gotten a book yet... But I know what I need to for DSP and SM
I forgot about the whole seat / carpet issue as I havent owned a s13 since 97' and the s14s arent like that

Just scrounge up the few peices needed and put then back in. But then again if you only run locally and never attend / plan on attending a nationals event youll be fine in SM, as your region doesnt give a **** it seems. I mean you dominated the DSP class in a what should have been SM car previously (that was some funny **** catching you hehe)...
edit: so yeah put the trim back in and remove the seat (which is SM legal) and itll weight even less, Im guessing, but still be legal, well sorta..