cj_bowling_ball3.wdr goes into: 
GTAIV\pc\data\maps\props\lev_des\minigame.img (Open and replace with OpenIV)

lev6_bowlball_b.wdr, lev6_bowlball_g.wdr, lev6_bowlball_o.wdr, lev6_bowlball_r.wdr, lev6_bowlball_y.wdr ALL go into: 
GTAIV\pc\data\maps\interiors\int_props\props_ld.img (Open and replace with OpenIV)

OpenIV Download Link: https://www.gta5-mods.com/tools/openiv

//////////////////////////////////////////////////////////////

Niko only uses the purple ball to bowl with, so that's why only 1 head is used to bowl. The rest are decoration props.

Enjoy you sickos,

- Maverix