Cryptoheros chetumalensis is indeed an available species name. In fact, the description is the result of splitting up C. spilurus into three species (the third is C. cutteri from Honduras). While C. cutteri is clearly distinct, the validity of C. chetumalensis is not convincingly demonstrated. If it is really valid as originally described, the name C. spilurus has to be deleted from the list of cichlid species occuring in Belize and has to be replaced by C. chetumalensis
As you have collected C. spilurus at Lago Izabal, the type locality (could you post some pics of your fish please?), you can be sure to to have the true one. So if you bring back 'spilurus-like' cichlids from Belize, you will be in the fortunate position to compare them directly.