The 60 III is a loop scavenged engine that was from the early 70's, with a steel sleeve and ringed piston, air bleed carb. The 60X is a schnurle ported AAC (Alum. ringless piston / Alum. sleeve / Chrome plated ) that came later and had a more sophisticated carb.
Enyas are great engines...the .60III is a good, reliable powerplant...not extremely powerful by todays standards (the .60X is a lot more powerful ) but a good, quality piece.
NIB would "probably" (maybe, possably
) go for around 75.00 give or take a few $