Drag And drop, Easy install :)

Original Unlocked model By: Potato Mods 

REPLACE 
mods\update\x64\dlcpacks\mpsum\dlc.rpf\x64\levels\gta5\vehicles\mpsum.rpf\

BOV & BACKFIRE
mods\update\x64\dlcpacks\mpsum\dlc.rpf\x64\audio\sfx\dlc_sum20