F103 bodies fit with some trimming on the nose. I'm not sure about f104 bodies. Hopefully someone chimes in on that. Really don't NEED any hop ups to be competitive, its that good out of box. I have got the alloy castor block, and will do side spring mod, but I'm running just as well or better than the f103s and 104s at my track.
I also opted for longer titanium links on rear.