I don't know about hard-to-find, but the exhaust gaskets on the Saab B and H motors really are somewhat expensive. IIRC, over $25 each for the 8v motors.

I've used RTV on a header on a Saab B motor with no problems, as header gaskets are unavailable for a Saab, but header flanges run cooler than cast-iron turbo (!) manifolds.

It would probably work, but I would suggest using RTV on an old all-metal exhaust gasket (if your model still uses that type) rather than eliminating the gasket entirely. That's if the gasket on yours also incorporates a heat-shield for the plugs, as was the case for the B's and H's.