I'm pretty sure that plymouth is going to have a closed driveshaft.Plan on using a driveshaft and rear axle to go with your 318...What you need to do is measure the distance between the brake backing plate flanges on your current rear axle and post it here..You can get some suggestions as to what fits..Since you will have to fabricate a driveshaft it really doesn't matter what make the axle is. Another thing to keep in mind is that there are two oil pans for the 318 if you need a different sump design to fit your application..