401k provisions effective in middle of plan year

[dmb]

A client had a calendar year profit sharing plan that was amended to a Safe Harbor Matching 401k plan with the 401k provisions effective 7/1/04. The client is a partnership and therefore has partnership income. Is it possible/legal to provide matching contributions on compensation earned from 7/1/04 thru 12/31/04 rather than the entire year?? And if so, is there a way to do that with the partners' income since they do not receive a salary?? Thanks.