Numbers matching

Selling our 2 1968 Barracuda convertible:
#1 383 4 speed Formula S convertible
#2 340 4 speed Formula S convertible
Have a customer coming to look and has asked me to check for numbers matching and or period correct.
I know how to check on the 60s and 70s GM but not Mopar.
I'm helping an estate to sell these cars.
Thanks
Dave