Here's where I am so far: I believe the six arched double loops each ending in a circle are similar to a 4-maravedis coin from
'Fernandvs et Eliabet' during the period 1474-1506. The obverse legend would read FERNANDVS ET ELISABET and REX ET REGINA CAST LEGION on the reverse. A lion is pictured on the reverse (at least part of one). If the reverse is rotated so that the "R" is in the 5 o'clock position, then the two rear legs of the lion appear more evident. I believe the counterstamp reflects a reevaluation, not an indication of the monarch.
Click on the highlighted "aqui" at the third coin down on this site to see a somewhat similar coin.
http://www.maravedis.org/reyescatolicos.html
What do you think?
Don.....
Edit: I can agree with Moe that it might be an "8" reevaluated as an "8"