Hi Sachin,
For DBM the profit center is determined for each internal order created at header level and split level which is passed to accounting document...I am not aware if in DBM 8.0 profit center is determined at item level..if this is the case then it should be from Material master.
what you can suggest is to group the items by internal department for example for bodyshop 2 items, paint - 3item for the same customer and determine the profit center by order type / customer combination.
But structure of DBM CO value flow is such that , i think you need to search for SAP note for profit center at item level ..else you will not be able to use profitability analysis since you end up one profit center at internal order of split billing and actual accounting document with difference profit centers at line item level