Personally, I am not of the opinion that any aluminum head is going to survive a severe overheat on a 603. The design of the head with very little material between the valves and the prechamber is the primary cause of this.

While the later heads improved the design with more material in the weaker areas, it's still not cast iron and any thought that it is bulletproof ought to be dispelled.

BTW, take a close look at the belt on the SDL. It might be three years old now..........and I would change it on principle. It's a 15 minute job if you're prepared and understand the belt routing.