Add following manually in shoppings.dat file:
To section prices - section CarMods:
		exh_a_wv		WVLAXH		respect 0 	sexy 0		700
		exh_c_wv		WVLCXH		respect 0 	sexy 0		600
		misc_a_wv1		WVLAFB   	respect 0 	sexy 0		990
		misc_a_wv2		WVLCFB   	respect 0 	sexy 0		980
		spl_a_wv_r  		WVLASP		respect 0 	sexy 0		900
		spl_c_wv_r  		WVLCSP		respect 0 	sexy 0		920
		wg_l_a_wv  		WVLAWG		respect 0 	sexy 0		900
		wg_l_c_wv  		WVLCWG		respect 0 	sexy 0		930

To section shops - section carmod1 (to make them appear in the mod shops):
		item exh_a_wv
		item exh_c_wv
		item misc_a_wv1
		item misc_a_wv2
		item spl_a_wv_r
		item spl_c_wv_r
		item wg_l_a_wv
		item wg_l_c_wv

Add following in gta.dat file:
IDE DATA\MAPS\veh_mods\weevilparts.ide

If you want to use the parts, replace string starting with club with this:
esperant, exh_a_wv, exh_c_wv, misc_a_wv1, misc_a_wv2, nto_b_l, nto_b_s, nto_b_tw, spl_a_wv_r, spl_c_wv_r, wg_l_a_wv, wg_l_c_wv