im building an ls1 for my 71' C10 pickup and im looking to get about 400rwhp. i have a good stock block and bottom end. i will be using the gm performance parts carb kit with the front mounted distributor. i have a demon 750 cfm carb. i will be purchasing a 224/227 custom ground cam, which was suggested by Shane at Thunder Racing for my setup. i am using a monster transmissions ss mega monster th350, 3200 stall and 3.73 gears. my problem is my cylinder heads i have a set of stock 853 heads. is it worth getting a valve job and porting or should i look for a different set.