I did some digging on the dealer's website and discovered the engine is a MO code witha June 20th assembly date...seems to line up with the 07B trim tag. Still, I'd obviously want a pic of the assembly stamp before inquiring any further. Even if the block is orignial it's pretty expensive for a car that appears to need a complete referesh.
Link to 1968 RS/Z auction
124378L347902