Church plan mergers - 401a/k merging into 403b

Does anyone has experience with merging a non ERISA church 401k or 401a into a Non ERISA Church 403b plan? This is permitted under Code Section 414(z) as implemented by the PATH Act of 2015. I am interested in the mechanics of how to do this - lets say the 401k is the existing plan, but the Church wants to have non ERISA 403b plan. Would the client need a Board Resolution, along with a new 403b plan into which the current 401k can be merged? I believe there is a requirement that all accounts that are merged be nonforfeitable - i.e. fully vested. I realize there are no regulations on this issue to date. Any thoughts would be appreciated!