This is simply a Yosemite with the tailgate removed and the bed replaced with the one from the Tow Truck, it should be fully functioning as a tow truck and is fully SA-MP compatible
Credits
Original Models and Textures - Rockstar North
Combining - Guth3D
Installation
Simply replace the "towtruck.dff" and "towtruck.txd" in your GTA3.img with the ones included in this download using an IMG Editor like SPARK
Replaces - Tow Truck