J par..... you tore your Duster apart like a model kit. There is really no more work putting a 318 mag where the LA 318 was than if you went to an LA 360. Same everything, and if you want to take a "sure way", get a 360 truck pan and pickup tube, and put them on your mag with the LA front. While the intake and timing cover is off, throw a cam with a snout in there and put it back together using the LA front. DONE! READY to RUN! PRESTO..... lol
P.S. - you will get a power increase. Best of all, you won't need to add extra Zinc