Wow that first pic sure did look like the C7SE-A number huh?? A little wire brush revealed the C7ME-A number clear as day. I have the same casting number on my block in the Coug. That said casting numbers are generic on most blocks. Once you pull the engine you'll see exactly what you have. And find the date codes that'll tell you a bit also. I'll decode them for you and you can compare it to the build date to see if they jive. My car has a Jan 8 68 San Jose build date. And the engine date codes are Aug 67. I've been told it's very possible it's original due to the strike and backlog of cars. Diverter valve has a Dec 67 date code as well as the smog pump which were added on at the SJ plant.
Once you pull the engine you can drill bit test the blocks cyl wall cores. Easy to do and that will tell you if there are std 390 or thicker 428 wall cores. You simply knock out the 6 freeze plugs in the block and use drill bits to gauge gap between the cyl walls inside. 17/64" is std 390 and 13/64" is 428. The date code for the block is below the oil filter adapter pad. Look for a number/letter/number(s) sequence. Head date codes are under the VC between the center 2 valve springs. Also note the head casting number between the center 2 spark plugs. The crank stroke you can either measure or see what numbers are on it. The 2U 390 crank is the most common to find. Very good too!