Put all dff and txd files in gta3.img. Then open GTA San Andreas/Data/Maps/veh_mods/veh_mods.ide with notepad.

Replace your strings (1001, 1003, 1004, 1005, 1006) with the lines below.

veh_mods.ide:
1001, spl_b_bab_m, vehshare, 70, 0

1003, spl_b_mab_m, vehshare, 70, 0
1004, bnt_b_sc_m, vehshare, 70, 0
1005, bnt_b_sc_l, vehshare, 70, 0
1006, rf_b_sc_r, vehshare, 70, 0
