Mid year merger of non safe harbor and safe harbor plans

I have a question in the M&A context - company B will be purchased by company A on 5/1.  Company B has a non-safe harbor 401k plan and company A has a safe harbor plan. What are the options mid-year - can the non-safe harbor plan be merged mid-year into the safe harbor plan? I would think best practice is to use the IRC 410(b)(6) transition period at least through end of the 2024 plan year and then merge at end of plan year? Or freeze plan B, allow employees to join plan A and merge at plan year end. Any thoughts?