No matter what rings you buy even stock style you will need to check gap. You may get lucky and not need to file them but you most definitely need to check gaps on the rings for every cylinder.

 

Of course, that was always in the plans to check with a feeler gauge but it seems like the majority of rings on the market are meant specifically to be gapped. I'm still running a standard bore and will be using a standard sized piston so a standard ring should at least get me in the ballpark (with verification of course).

 

Okay I'm editing and bringing this post back to life now that I'm at the point in the engine assembly to order rings. Definitely going to be checking and gapping rings as required so I'm no longer worried about that. Unless anyone else has a suggestion, I'm pretty much now at the point of looking at either Mahle's 42084CP or their 42157CP which both Mahle's catalog and BTR's site spec for a 4.000 bore LS motor with the 1.2mm top ring, 1.5mm second ring, and 2.5mm oil ring that I've measured on my stock LS2 pistons. Seems like pretty much the only difference is the radial width of the oil control rings on them but the problem is the radial width listed on either of them on BTR's site doesn't match the measurement of the oil ring radial width of my old piston rings. 42084CP is stated to be .123 radial width oil ring, 42157CP is .110, and I'm measuring .090" on my oil ring. Now the ring gland depth of the piston for the oil ring measures .123" so with clearance I'm assuming the 42157CP .110 radial width one is probably what I need.
Asides from physically measuring though, most sites I've found, like Rockauto, list the 42084CP as being the correct one to go with. There's some fast GTOs on this forum though so I'm sure someone's done this before that might lend some insight.

 

Well as an update, Mahle's 42084CP is NOT right for an LS2 piston, at least not an LS2 piston out of our GTOs. The top ring and 2nd ring were good but the oil control ring radial thickness was too large like I was concerned with on my last post. I tried discussing this with Mahle's tech support but they basically gave me the standard auto parts store excuse of "well it says on the screen those are the right ones". I'm giving up on Mahle altogether and trying Sealed Power E979K rings which Summit shows as working and has some reviews saying it worked in their LS2s. Mahle's 42157CP set might work but considering the abysmal feedback I got from them, I'm not going to bother.