what credentials are needed to compete?

You might fit in NMRA Pure Street, similar to FFW Trophy Stock, yet a little 'looser' with the rules,ie long tubes, porting allowed, etc.
As for documentation, it depends on the class. Most of the time, you don't need diddley squat, except for required safety equipment (ie helmet for 13.99 or quicker,etc.).

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'91LX coupe.3.73's,alum dr shaft,subs,upper & lower ctrl arms,90/10's
1 5/8 long tubes,2 1/2" exh-off road H-pipe,pulleys,ported stock t-body
ported cobra intake,ported stock heads,B303cam,77mm mass air,
12.503 @ 107.93 mph on Nitto drag radials- Toronto, Ontario, Canada.