Two-bolt flange, but perhaps they have something similar for 3-bolt applications. These replaced the rotted flanges on my so-called "stainless steel" Edelbrock shorty headers.
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The two long bolts clamping the donut are in fact way TOO long. They were what I had on-hand at the time. I used some plain ol' 1/2" hex nuts as spacers to take up the extra length, and then double-nutted the assembly to prevent loosening. Ugly as sin, but also nicely-invisible unless you're under the truck.
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Permatex is big on promoting their "high temp" orange RTV Silicone; including it's 750-degree "intermittent" temp limit. I've asked Permatex reps twice about what is considered "intemittent" use (how long before it's considered "long-term" use) and what the long-term temp limit is. Both items are TOP SECRET and they WILL NOT ANSWER ME.
Normally I despise the stuff, but there's no sealing that bigass gasket for the two exhaust pipes/two catalytic converters on the Vortec engines without heroic measures. So when I need an exhaust sealer, I use Waterglass in the form of Permatex Muffler and Tailpipe Sealer, good for up to TWO THOUSAND degrees.
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