I may have asked this before, so forgive me if I did. During the Sun record days of Elvis, all the music coming out of there was called rockabilly at first. Blue Moon of Kentucky was rockabilly for sure. Country music was country/western, now it is mostly pop with very little twang and nasal. Bluegrass still sounds the same (although I can't define that either). How would you put together/write a rockabilly song today. I don't mean what instruments do you need. Musically, what are the necessary ingredients?