As far as casting dates, a lot of '68 Hemi cars got blocks that were cast in '66.
Hemi blocks appear to have been cast in "runs", and banked for future assembly.
Possibly banked again for later installation, but I don't know about that - or for how long - with certainty.
That 1 sure looks like an I to me too, with its upper serif; an odd mistake to make, by whoever did it, but certainly suspicious.