1968 Dodge D200 with a 318 from who knows where

LA 318 started in 67 and the timing mark was on the pass side thru either 69 or 70 when they switched to the driver's side. You say your outer ring is gone on damper? Then so is the timing mark. But yeah the pass side timing mark ones had a cast iron water pump.
'68 truck, 68 engine what makes you think it's not original? They didn't put vin numbers on blocks either until 69 or 70 and no, the number after "PM318..." wouldn't be the (partial) vin even if it was numbers matching, the vin would be on a machined flat spot just above the oil pan towards the back and as I remember pass side of the block.
Also how many people have had this truck since Seattle was done with it?
Aluminum manifold cracked (where you say it did). I'm quite far from having seen everything but I have never heard of that one.