Joe: I don't believe the "F" stamped into the toe of the stock on your Gew. 88 has anything to do with a regimental marking. The regimental marking, if present, should be stamped into the side of the barrel band. The regimental marking will be a series of numbers and/or letters separated by periods. The regimental marking will normally identify the specific regiment, company, and inventory number of the weapon within the regiment.
I will try to research the meaning of the F in the stock.
Reservist1