Calculation of Grandfathered Amt. in a Non-AB Plan

[smm]

I need some assistance in determining a grandfathered amount in a non AB plan. Plan provides that participants receive a pro-rata share of an aggregate amount (determined pursaunt to a very complex and non-discretionary formula that is set forth in the plan). The formula is based largely in part on the compensation paid to all participants in the year prior to the year in which installment payments from the plan begin (which is on termination of employment). (I'm paraphrasing, of course) Plan was in existence during 2004 and all participants were fully vested at all times. Regs say that it is determined as if the participant voluntarily terminated w/o cause on 12/31/2004.

Thanks.