WACC of Combined Firm Calculation

I'm trying to value some synergies and discount them back with the WACC of the combined firm. I know I need to find an "industry beta" and then lever it with the capital structure of the combined firm. Obviously for debt I just add the debt on the b/s of the individual firms and add any new debt needed for the financing. What do I do for the market value of equity weight? Do I add the MVE of each firm from before the acquisition, or do I take into account the premium paid? Thanks