Install the txd and dff files as per with any vehicle mods or use the GGMM to install with handling(not tested)
I have added my weapon dat file to upgrade the MP5, M4 and Country Rifle versions of the weapons,
these are mostly accuracy and distance related apart from major differences for the L86 version.
Just copy and paste this into the data folder or copy and paste the specific parts from within that you need.
The uprated stats only apply to hitman level, the L86 is upgraded from the off however.
Enjoy.