i'm fairly certain the cooling water only comes thru the hose on the end of the manifold, not thru the cylinder heads. automotive gaskets should work, but i'd compare them very closely to what you have now.
i assume that was a stealership that quoted $250? check skidim.com for good prices.
that said, there's NWIH i'd go thru all that trouble to repaint them. the paint will burn off again in the first couple hours of use.