Do as much diagnostic tests as you can before pulling it apart. Remove all the spark plugs & check their condition. Carry out a compression test while the plugs are out & check for variations between the cylinders as well as the actual pressure.
I would just leave the stamped numbers alone if you file it all down and restamp it the stamps you use will have a different font and it will be more suspicious also there are marks left by the original machining if it is filed down these marks will be removed and the area will come out too...
If I already owned it I would use it as is, if it was for sale I probably wouldn't buy it (too early for an E body anyway) better to buy another block without the messed up stamping.
Nothing wrong with the wheels just needs the earlier style centre caps. 8 3/4 rear axle would have been fitted to an original car unless A32 was optioned.
1970 Plymouth Barracuda -- | eBay
This looks very interesting wonder what it will eventually sell for? very similar to my 440-6 car except for the engine and mine is a Torqueflite also but mine has the A32 Dana, love EV2 cars.