Acquisitions with a SIMPLE and a 401k

I have a client who is starting to grow through acquisitions.  Client sponsors a SH 401k. They have purchased a Company (Stock purchase not Asset). New firm has a SIMPLE. I know there are transition rules that allow this arrangement to continue through the end of 2023.  They are about to complete another acquisition (or more) as Asset purchases. The target has a 401k and they want to allow that new staff to join when acquired.  I believe the SIMPLE has to continue and that staff should not be eligible/contribute to 401k

If they amend the current Plan to recognize the new group(s), don't they lose the 410b6c exclusion that allowed the first acquisition to complete the SIMPLE for 2023? Can we amend to only allow the asset purchases to enter the Plan early? Any guidance is appreciated!

Yes, you can amend the 401(k) to immediately cover whatever specified acquisition group you want, and then lose the 410(b) transition period. If you can satisfy coverage for the 401(k) on that basis with the SIMPLE people not excludable but not benefiting, no worries. 

How about testing by parsing out those otherwise excludable?

Thanks for the response. As for testing, I have not seen any census data for the proposed acquisition(s).  Currently, it is a very small employer so if there are not any OEEs, coverage may be an issue with any exclusions.