if you are going to swap an engine into your impala, I would recommend doing an L32 if you can find one for a reasonable price. the L67 is ok, but the L32 is better. as for headers, I recommend the ebay brand. SSC, OBX or Speed Daddy are decent. Right now the price is high because they are low on stock, but when they get more in the price will come down to around 250-300. the only problem with these headers is the interlock flex section, the flex section is a bit too long so the downpipe ends up dropping down a bit low. I have a set I am going to modify with a shorter flex section I think its like 2.5" long.