^^^^^He's right.
LL29C1B is the start of a V.I.N. for a '71 225 slant 6 Demon.
You have a Demon if the fender tag and the other numbers that are stamped into the core support match the last of the V.I.N. numbers.
The fold down seat option is obviously added, as well as the upper and lower dash pad combo.......
A lot more pics would go a long way here.