Hi Lightning,
Be careful not to confuse required equipment (Part 27 or the Schweizer equipment list) with an MEL. Put in somewhat oversimplified terms, the MEL is a list of the equipment than can be non-functional but still allow the aircraft to fly. For the Schweizer, the equipment you list is required by FAR Part 27 (except for the OAT, which is on the TCDS Equipment List as required equipment), so could not be on a MEL.