Walker #31311. Same flange both sides. I'm not sure if Walker still has these, but they are out of my old Walker book. NAPA exhaust IS Walker, so these #'s will reflect the NAPA #'s too.

I just looked online - looks like these are available almost everywhere. They are a 2-hole flange.

EDIT: 31311 is a GASKET, NOT the flange! That being said, I was able to look up the dimensions: opening is 2-7/16", & center-to-center of the bolt holes = 3-29/32". When I look into the gasket & flange usage chart at the back of the catalog, the gasket does not show a corresponding flange. I'm still looking so stay tuned. Looking in my ROL catalog next.

OK, looks like these two ROL #'s should work - these are FLANGES: Type 7 style (2-hole flange) - SF69023 - it's 3-29/32 center-to-center, & 2.5" hole, but 5/16" thick. Next one looks better: Type 7, part# SF66045, 3-7/8" center/center holes are oblong, opening is 2-9/16" & this one is beefier 3/8" plate.

OK - more options (this is growing isn't it?): Since ROL may be out of business, I'm in a Goerlichs (AP Exhaust now) installer catalog. Here's a NICE-looking stamped & contoured flange: #9164. See diagram. Dimension A = 2-9/16". Dimension B = 3-15/16".