KincardineCJ3B,
I'm going to go out on a limb here.
My initial impression is this F-head is not originally from a CJ. The dipstick is unusual and the distributor has a vacuum advance on it. I don't believe CJ-3B's had a vacuum advance. Also, the draft tube is, from what I understand, replaced with the Positive Crankcase Ventilation system on the CJ-3B.
If I were to guess, I'd say this may be a truck or wagon engine - I just don't know for sure (I haven't been exposed to that many engines) but others may.
I don't recognize the clutch. It also looks like some repair work on the generator adjustment arm too. I'd also like to wager that on the driver's side where that 90 degree fitting is should have a plug and under where the pump mounts is what I'm used to seeing for where the oil line attaches.
For me, finding the serial number (located on the front just above where the water pump attaches) would be the first place I'd look and then compare that number with the engine numbers on the 3B Page.
That engine may work (not sure about the clutch) just fine as a 3B engine. Do you knnow more about it?