ARP rod bolts on 6.1 - head size?

That's odd. I have arp's in a 5.7 with no issues at all. The 5.7 and 6.1 are the same stroke. Didn't think there was any difference in rods either, not 100% on that. Wow, wish I could be more help. Have you switched bolts around randomly to see if you get clearance?