The same way you would make any car mod for tdu2. Just instead of starting with a 3d model you made/ or got from say forza, you are using a model you have previously extracted from tdu1. There are plenty of tools for unpacking tdu 1 and 2 files, so you would just one of those. then load the mesh into zmodeler and make it like you make any tdu2 car (however that is done)
Also the sounds are pretty poor (I'd even say they're worse than mine, really...) Especially the ferrari's got some honky idle (That just needed some EQ), messed up deceleration samples, and some midlow RPM pitch issues. Also the rims on the Huracan are messed up. It's not up to the Unofficial Patch standards by any means. I do appreciate checken's effort however. I'd just preffer one single perfectly working car over three poor ones.
I didn't know about those two patches, and intalled the chickenpatch just some hours ago and, I have to say, I'm hugely disappointed. I've just tested the Huracan and the Ferrari, and it's not a "finished product" by any means.
The cars seem overly fast for some reason (unless that's just me), as if the weight hasn't been set properly... Also they are completely unpaintable, even in the paintshop (Matte is stuck in white, Metallic was adjustable until I switched it to bicolor and now it's completely stuck in a particular shade of Blue, Glossy's stuck in Black, and carbon in gray. And when you exit the paintshop it doesn't get saved -.- The stickers do save though...