merger of off calendar year safe harbor into calendar year safe harbor and transition period

My question involves the merger during the 410(b)(6) transition period of 2 401k safe harbor plans with the same safe harbor match but Plan A has a plan year ending 9/30 and Plan B is a 12/31 calendar year end plan. The goal is to consolidate into Plan B by 1/1/2023 since the coverage transition period ends 12/31/22. What is the best way to accomplish this? Options I see are 1. freeze plan A 9/30 and adopt Plan B on 10/1 (transition period ends but does it matter?) so participants will be in Plan B with mirror safe harbor match, and then 12/31/22 merger Plan B into Plan A, or 2. change the plan year of Plan B to a short plan year from 10/1-12/31 and maintain safe harbor status, and then since both Plan A and Plan B will be calendar year plans they can merge on 12/31/2022. This option creates 2 5500's as well,  a plan amendment and also the need for new safe harbor notices for the 10/1 short plan year, so it appears more burdensome. I do not think create a short plan year violates the transition period rule? I appreciate any comments, thoughts, help since I have not really had this issue post-transaction. Thank you!

I think the first choice is easier. Just make sure Plan B provides service credit and has an appropriate entry date (all as needed) You'll then provide the Plan B SH notices to the Plan A participants to enroll.

When you merge the Plan A into Plan B, you're still creating a short plan year and 5500 filing for Plan A.

What if I merge Plan A into Plan B on 9/30 which coincides with the end of its plan year? Are there any issues? Both are safe harbor with the same basic match formula. THanks!

What if I merge Plan A into Plan B on 9/30 which coincides with the end of its plan year? Are there any issues? Both are safe harbor with the same basic match formula. THanks!

The transition period will end on 9/30 for both plans, but not sure that is a concern - any thoughts on the 3rd option?

I don't see it as an issue.

Thanks!