Next you must go into the files of the physics mod. Go to "disk/wars_patch/character".
Depending on the character you want you'll have to extract the following.
Classic Sonic - "sonicclassic.pac/sonic_classic.rfl" Modern Sonic - "sonic.pac/sonic_modern.rfl" and "sonic.pac/sonic_modern_topview.rfl" Avatar - "buddy.pac/gadget.rfl" and "buddy.pac/gadget_topview.rfl" Super Classic Sonic - "supersonicclassic.pac/super_sonic_classic.rfl" Super Modern Sonic - "supersonic.pac/super_sonic_modern.rfl"
To extract the files drag the pac file into SFPac and then a folder will appear. Finally, take out the files seen above for what character your trying to make compatible.
Then find the same pac file for the skin you want to use. Extract that into a folder and drag and replace the rfl files you extracted from the physics mod.
To repack the skin drag the folder itself into SFpac and it will create a new pac file. This one should now contain the skin and the physics.