2951123 manifold on duster?

They'll physically fit the 340, but 318 exhaust manifolds have smaller ports and outlets (i.e. more restrictive) than 340 manifolds.
https://www.bing.com/ck/a?!&&p=4574...21vcGFyX2V4aGF1c3QtcGRmLjE3MTQ2NjcyNDYv&ntb=1