Your "K" coin is Byzantine. It dates no earlier than 498 AD when Anastasius introduced Greek letters on the reverse of coins that indicated the value in 'nummi'. M for 40 nummi (a 'follis'), K for 20 nummi (half follis),etc. These reverse images (letters for denominations) were in use for 300 years.
The obverse may show Anastasius I facing left. The lettering would be ANASTASIVS PP AVG. The cross may be situated between the letters N and I.
Don...