StorminMatt

The rear cover bolts on my LS1 are M8x30mm. But the bolts in the ARP 434-1504 set that I got are only 20mm long. Which are the right size?

Jontall

I'm almost sure it's M8X1.25X24, but GM has 2 part numbers for the rear cover and I listed the bolts that come with the newest cover. I don't know the length of ARP 434-1504. A brand new cover with bolts, seal and gasket GM part # 12639250 is ~$50.

StorminMatt

Actually, I was able to confirm from two GM dealerships that the correct length is indeed 30mm. Not sure how ARP messed this one up. But they agreed to exchange the set for 12 M8x30 bolts. Hopefully, they will change their set so that it includes the right boots.