That is a sweet EG 303!
It looks like a Savage checking pattern to my eye. After market patterns can be nicely done, but, usually contain obvious differences from Savage patterns.
Up to that point in time the pistol grips like the 99G had 2-point checking as standard. Possibly plain.
Your early EG has the same type of pistol grip and 3-point checking. Possibly fancy.
EG's thereafter have 2-point checking. Possibly plain.
A factory letter might just indicate "checked" or abbreviated "CK" since it was an adder at the time.
Without definitive knowledge or a catalog/advertisement, the plain/fancy checking is just a guess on my part.
