To install you need OpenIV, then just open vehicles.img and make sure you are on edit mode and then drag and drop the files in there.
Then open handling.dat and find Moonbeam and change the line to:

MOONBEAM 2500.0 0.00 80 0.0 -0.10 -0.4 0.0 5 0.135 1.0 143.0 0.16 0.64 0.30 33.0 1.10 0.90 14.0 0.15 0.4710 2.5 0.9 0.9 0.15 -0.16 0.012 0.48 1.0 0.6 1.2 1.5 0.0 22000 4008 0 2

Optionally you can use the highway hayosiko skin (yellow van skin) instead of the regular blue skin.

Enjoy.

Credits

APoliteCat - for making the mod thumbnail in GTAInside
Amistech Games- for making the car
GTA Mods Del Norte- for porting the car over to SA
CarCrasher730- for porting the car from SA to IV

Changelog:

0.1
Fixed the colors
Added handling

0.2

Added alternative skin

0.3
Fixed door collisions
Removed unused vehicle reflection texture

0.4
Fixed a cap in the wheel
Added a fixed config that is made of mirrored version of bodyshell and chassis but it has a few bugs, like lights being hidden under the bodyshell and the front cap being closed off
Aligned wheels

0.5
Finally fixed all the culling/gaps issue
Readjusted some of the dummies and pivots

0.6
Fixed some polygons of lights being left in the bodyshell and connected them with the lights