Level 3 is the closest equivalent to NIST SP 800-171. CMMC Level 3 includes all the NIST SP 800-171 requirements with an additional 20 practices and three processes.
Level 3 certification may be a concern for many contractors. If so, determine whether or not there is an actual need to meet Level 3 requirements, as it’s possible that Level 3 will not be required for the contracts in contractors’ pipelines. Consider discussing such with contracting agencies, but do understand that they may not have an answer at this point in time.