It's my understanding the ARP studs are a little shorter than the A1s. In order to achieve full thread engagement between the ARP stud and nut, one has to mill the pedestals a little to gain the clearance needed. The A1 studs being a little longer, have enough thread for full thread engagement, but often require relieving the valve-cover webs because of the stud's extra length.
It's my understanding that, as a general rule, to ensure full thread engagement, one wants to see at least one full thread above the nut. That full thread should NOT include the initial, tapered threads.
At least, that's what the voices say.
When I was shopping for the things, I actually called and spoke with some German engineer with A1. He wasn't really familiar with any so called "Kit" for a given vehicle. They, (Like ARP) are a fastener manufacturer. They make the crap for anything, and everything. These Kits you and I buy, are nothing more than a collection of the right size nuts and bolts, of a given material, that meets a design specification. And those components are more often than not, Off-The-Shelf parts for them.
