Superbirds are roadrunners...so RM23 are the first 4 digits...then either U=440-4, V= 440-6, or R= hemi. If you find a fender tag, post it and we can decode it. If no fender tag, here are some things to look for:
look for the K-member skid plate...all 440 and hemi cars have them
look for the inner trunk wing supports...they helped the rear quarter take the load of the wing. Even if they were removed, the signs of them might still be there.
look for signs of the A pillar molding, or of the vents on the fender tops.
If it's a 4 speed car, it should have a dana 60 in it.
I'm assuming that what you are looking at is a shell, with no nose or wing.
You can also get the VIN and contact the winged warriors club, I believe they have a list of daytona/superbird production.
Good luck! I've been persuing a superbird stored only a mile away from me for over 10 years..has not moved since 1987. maybe someday the owner will realize he'll never get the car on the raod again, and give in to me and sell it.