Avanti emerg. brake cable clearance with R3 exhaust manifolds

I dont know about cable availability but if you housing is not totally shot why not just replace the innards and theen you can grease the cable with hightemp silicone grease. The automotive stuff is good for around 500 degrees but you can get stopcock grease from severa; pharmacutical suppliers that is good for a thousand and that should be pleny good for your application.