Quote: "I manage to work about everything except characters and weapons but other work well"
FWIW, I've spot-checked several X9 weapons and most are able to drop into GG with relatively little changes.
For the most part, they just tend to look plastic wrapped as they generally don't have normal maps or specular maps (the now-stock fantasy weapons also have this problem). The plastic look can be diminished by reducing the global specular slider although that's really not the most ideal solution.
Another common problem is with positioning. I find that the gunspec settings for
forward=x and
simplezoommod=x each need to be increased by around 5. That usually does the trick if the weapon FOV slider is set to around 60.
You will also need to replace the crosshair.dds with a GG-compatible one (swipe one you like from a known-working GG weapon).
There are several other differences in gunspec but they are generally fine tuning tweaks because some of the input ranges are different. The notes above will usually get you going in the right direction though.
For pickup items, basically just follow the FPE settings for the stock stuff and assign the appropriate lua script.
Gigabyte P67A-UD4-B3, Intel Core i7 2600K, 16GB Corsair DDR3, EVGA GTX 970 SC, Win7 Pro 64-bit SP1, Primary monitor @ 1920x1080, secondary monitor @ 1024x1280