it meant that most shifts were invalid due to invalid base58 characters but I did get a few valid private keys
Huh? You shouldn't have been able to do that, a random set of characters beginning with the right byte has a shockingly small chance of being a private key. It's like one in 2^32 due to the checksum.
ahem, allow me to restate: i got some apparently fine looking keys in proper base58 form that the python bitcoin libs happily transformed into private keys and public addresses, but a real bitcoin wallet failed to load properly.
no clue why it would be there otherwise.
Ditto the numbers "outlined" on the right hand side of the image.
yeah, definitely.
I guess I am back on the thought that if the 51 char string is not something we can shift into a private key, then it must be some kind of 37337 clue and we're looking for a spoon in a haystack with bitshifts and the like.