Jeff, for the driver side head digit, is it in white or yellow crayon? would this be similar to what I see on 428 photos (most of those seem to be a yellow S and the 390 would be a digit)?
Looks to be in white. In this case the number "2" You can make out the top part of the number at the top of the picture faintly
There is also a hortizantal line that keeps showing up on the from of FE engines in the 68-69 period. I've seen them on the drivers head under the ID sticker, front of the drivers side valve cover (painted ones) and on the drivers side head (front face) just under the valve cover. Since we see them in multiple locations they all served the same purpose but applied by different workers/inspectors
Here is a shot of the OK in the box applied to the valve cover. Should not make a difference that this engine wasn't ordered with the chrome dress-up option
Hope this helps ... just hope posting them doesn't mean we'll see these on every 65-70 Mustang next year at shows