I have a 292 block that has been bored 60 over, each bore is 3.935 in. I ordered a set of rings for it, Summit part no. SLP-E-217K60, but when installed the ring gaps are about 0.030 (between ends). I was told by a knowledgeable man (Moog ring engineer) that the gap should be 0.013 in. Is the difference enough additional gap to worry about? I.e., will I have excessive blow-by or other issues?

I have not been able to find I6 rings that are slightly larger, that could then be end-trimmed to get the 0.013 gap.
Thanks.

Talk to Total Seal!! They'll have what you need AND the pertinent information to go along with it! They can make the rings you need if they don't have what you need on the shelf!!

Your knowledgeable friend is spot on. When I got my ring package from the guys at Ross Pistons - the compression rings provided fit the bores perfectly with zero clearance. The ring manufacturer (Hastings) documents the minimum clearance based on a formula published here Hasting Service Tips. It calls for no less then .0035 clearance per inch of bore diameter. A few minutes of filing and they are right to spec . . .

So I am with Blackwater - the manufacturer of the rings must specify the gap based on the expansion rate of the materials they are employing.

In the case of Hastings rings a clearance of .030 would be perfect for an engine with 8.57" bores!