For Martin :-to quote a great man "If you knew your history you would know where you're comin' from". Marty Robbins heard Elvis' regional hit of That's Allright Mama and because he was on a National label (Columbia I believe) he copied it ( look for the recording dates Elvis' was out 4-6 weeks before Martys ) and sold many more copies to have a national hit. This is confirmed in all serious volumes relating to the musical landscape of the period an was a far from unusual occurrence. Also,I think Marty himself confirmed this on several occassions.
For interested parties:- Big Boy Crudups' version is in the key of E. Whilst Elvis' is in the key of A. The only two versions worthy of consideration.