Using 6.1 heads on a 5.7 block also requires the use of 5.7 head gaskets. Yeah, not perfect, but the 6.1 heads were the heads that were submitted to NHRA for their 5.7 engine package. I wish the 09 Eagle heads were submitted instead, but it is what it is. However, NHRA will allow the 5.7 to be overbored to 3.995 which will be much better.