I know (by nearly crashing my bike) that the cleats for Shimano Ultrega PD 6610 pedals click into but will not disingage from Look pedals. I am wondering if these Shimano cleats will function with older Shimano (PD 1056) pedals, even though they are marketed as Look compatible or "Look alike" if you prefer.

Thank you for any assistance you can provide.

No, I don't think so. SPD-SL is intended for use within its own competence only as far as I'm aware. It's a risky business mixing pedals and cleats that weren't designed to be mated. Personally I would stay well clear. Either buy a set of 6610 pedals or a set of 1056 cleats.

The old Shimano PD 1056 are Look pedals with Shimano's name on them, and you use Look delta cleats with them. Just use the RIGHT cleats with the RIGHT pedals.