Yes you would need to change the files for the PC to a xbox version.
If you were wanting to put a car that was made for the pc into the xbox version heres how
1.Get IMG Tool
2.Open Gta3.img
3.Open TXD Workshop
4.Open a .TXD
5.Click either VC XBox for san andreas (xbox) or just San Andres (For PC only)
6.Save
7.Go back to IMG Tool
8.Replace the car you want to put in
9.Save it
10.Upload the gta3.img to the xbo
11.Clear X: Y: Z: and E:\Cache
12.Enjoy! :)