Those are probably socket head cap screws. My DSM had them stock, also 10mm. Stripped the teeth on my flex head ratchet. 2ft snap-on breaker bar and really had to lean on it. I'd say I put at least 200ftlbs into getting them out.

With an aluminum head I'd be suprised to see the torque spec be more than 80-90ftlbs, but if the ends of those bolts go into the water jacket there may be some rust holding them in too.

John C.