I live in Falls church and I too have a Irish green 912. While I don't have any running motors I do have lots of motor parts from heads to cranks, rods carbs and the like. Lots of other parts as well.
5 speeds are not hard to find but if you have the early outer hubs you will need to convert or adapt the axles. For street driving the 4 is fine.
Lucky you! You live right next to a great ten turn race track, Summit Point. My 912 has spent many a day at that track p!ss!ng off early 911s.
Your going to have to change your screen name to reduce confusion if you want to buy any of my stuff.