Original Message

A model has a 250-C18,  the 500C had a 250-C20,  500E a different roterhead and blades I believe and a T-Tail 250-C20B, more sex appeal.

OH-6 could have a upgraded Engine, but you still can't use a OH-6 for a Private, Commercial or Flight Instuctor certificate, unless they have changed.  500C's are good to go for certification rides'