What to put on these threads?

On the stat housing I would drawfile the chrome off of the sealing surface. Wouldn't hurt to drawfile the manifold stat housing flange also (put a rag inside to catch fileings). dont overtorque the 2 bolts & I've had to use "the right stuff" gasket maker & a gasket to get em to seal tho technically TRS is a gasket maker as opposed to a gasket cement. drilling/tapping for new bolt holes at 6/12 0'clock is an option, for sure would not look OE but might do the job (ain't tried it yet). any antifreeze leak is a PITA