If you want to add the vehicle with Limit Adjuster and Model variations you can drop all the files in the modloader folder and make sure you pick the ID in the vehicles.ide line. Also add the vehicle audio settings line so the engine sound can play as it is intended

Handling.cfg
VOLPE 1500	2400	2.0	0.0	0.0	-0.1	80	0.70	0.80	0.5	5	200	28.0	10.0	R	P	6.0	0.50	0	35.0	1.0	0.07	5.0	0.25	-0.10	0.45	0.0	0.38	0.40	15000	C0002000	00000002	1	0	0

carcols.dat
car4
volpe, 87,87,0,0, 1,1,0,0, 105,0,0,0, 3,3,0,0, 65,65,65,0, 0,0,0,0, 79,92,79,0, 25,25,25,0
end

vehicles.ide
#####, 	volpe, 	volpe, 	car, 		VOLPE, 	VOLPE, 	null,	executive,	5, 	0,	1f10,		-1, 0.67, 0.67,		0

carmods.dat
volpe, nto_b_l, nto_b_s, nto_b_tw, spl_b_mab_m, spl_b_bbb_m, spl_b_bab_m

vehicle audio settings:
volpe 0 93 92 0 0.9 1.0 2 1.25992 2 2 7 0 31 0.0