1968 Dodge D200 with a 318 from who knows where

Alrighty then, I checked all the engine numbers and the casting number, 2536030 318-6 means it is an LA 318 built between 67 and 75. The 8 digit number stamped on the block below the drivers side head is PM 318R 25020444 which does not match the vehicle identification number on the tag inside and behind the drivers door. Unless this tag was changed at the time of an alteration, this may mean that the original engine was a LA 318?
If that's the case, why scarf out and replace the transmission frame support and what's with the patches on the holes in the front of the cab that align with the master cylinder brake and where a clutch rod would have protruded through the cabs forward wall?
Anywhoo, none of this changes my issue with the timing cover and the harmonic balancer.