my buddy's roadmaster did the same thing and i wound up replacing the entire thing with a new alum. radiator and electric fan set up. good thing because when he wanted an LS in it that was one less thing to worry about.
roadmaster is a sweet ride. he's got all hotchkis underneath and it surprises a bunch of people on the highway.
Awesome on a LS, I'll do that if engine ever needs replacing while I'm alive. It does get after it as is for a road trip car, Grapevine in 3rd works well and I like my experience so far with electric trans as opposed to 700R4 in my K5.