Use a new gasket with the new head. If the old one is in good shape you might get by but why waist the time since you know a new one will be good. the shims are used for compression adjustment the more shims the less compression at tdc. they also aid in timeing the combustion. I dont have enough experance to guide you through but post or search in the engine section about head shims and you will find wether to add shims or take them according to the engine operation.