From DB to SH 401k Plan

[DP]

I have never worked with DB plans and know very little about them. We have a prospective client who has an active DB plan which he is wanting to terminate. He then wants to adopt a SH 401k DC plan and rollover the DB balances into the new plan. His former TPA will handle terminating the DB plan.

There are five employees who have reached retirement age and are receiving benefits from the DB plan. They are also still working 1000 hours a year. Can these five employees be excluded from the new SH 401k plan? One of the five is an HCE.

What is handled differently in the administration of this new plan? Are the contribution limits the same?

Thanks for any advice.