thats model, CG-144 is a 5/8 over a 1/4. I cant find a colinear for mobile but did find this stacked 5/8 colinear for base application. Base Model G7-144 with 7dB gain. If that 7dB is true, thats more than some directional antenna, pretty cool, I might try to build such a thing. Is co-linear the same as co-phased?Not sure about 7/8 but Hustler makes what I believe is a colinear 5/8 (two 5/8's put together one of top of the other) Any Hustler dealer should have them. Ham Radio Outlet sells them.
The 3/8 x 24 threaded is model # CG-144
Trunk Lid Mount is # CGT-144
I've used one in the past. Work well. Best if you can locate in the free and clear.
Good luck
Keep in mind, the more gain, the 'flatter' the radiation pattern gets....it gets narrow as a razor. On flat, open ground or slight elevation advantage, this can be great. In varied terrain with rolling hills and buildings, this can actually hurt you vs a much higher angle of radiation on a no or low gain antenna.