Bill,
Any chance you can find the block casting date code? If the location on the low pressure engine is the same as the location on later engines, the date code would be to the lower left of the ledge to the left of where the distributor enters the block.
Just about any combination of low pressure head and block is possible. Owners just did what needed to be done to keep the truck running. Also, it looks like during that period the same head code was found on 216s and 235s.
That block date code would provide a useful clue.
Tim
