I have a few Fischer pieces (crowns and BB shells) and I do remember some numbers cast-in sometimes, but I don't remember details. Not at home to go looking at them now. My shells are the kind Masi used, without the "swelling" around the openings for the threaded cups.
The RR dropout has the "land" for the extra spring hole for Campy Sport derailer, but not the hole. Roughly speaking, DOs with the hole stopped showing up in the early '60s, but the land for the hole continued until they made new forging dies without the land, in the late-'60s I think. However individual makers could have continued using older dropouts for some years after they were gone out of the pipeline from Vicenza. So it's only a rough indicator of age.
If the tubes are inch rather than metric, then 26.8 indicates either a plain-gauge ST or a somewhat heavy single-butted one, with slightly less-likely options including a
double-butted ST (more common on Japanese bikes) or one with an internal sleeve added at the lug, á la Cinelli.
That's all I got! Cool frame though. Keep us posted if you find out more.
EDIT: I'm reminded by this pic from ebay, that the cast-in numbers are raised ("outies"), not sunk, so they are often filed/sanded off if the shell gets any cleanup. Same with the crowns -- raised numbers that almost always get removed during cleanup.
This shell is newer than yours though, so older ones might have had different numbers or styles.