To the untrained eye there's not a huge amount of difference between the F3 cases and the standard cases. Obvious differences are blocked off oil injector, LH side machined for F3 ignition and a couple of bored cutouts in the top cylinder case.

F3 cases are not exactly in surplus (I don't have any more), but if you can steal a look into a set of NF5 cases you'll get a very rough idea of what the F3 case is all about. However, the RS case if not the same and is further developed. Much further developed, but still not perfect IMO and can be improved upon.

I did haver some pictures of the F3 case, but can't find them now.