Originally Posted by Bigford99
what would the mods consist of? Would he just be better off selling them and order a set for a 400? thanks
The standard lenght rod bolt is a bit over an eighth inch longer than the 400 bolt. The 400 upper shank lowers the bolt by that amount. This will put more of the unthreaded length into the cap's bolt bore and will hang the threaded end .140 inch further toward the pan rail. I don't have a 400 rod handy to compare but the problem areas could be not enough thread to secure the nut properly plus I'd expect the extra bolt length will interfer with the pan rail as this clearance on the 400 is already tight.
You can always mock this with the ARPs in the 400 rod and check it out since he can't take the bolts back anyway so putting a few scratches in their finish isn't going to result in not being able to return them.