I happen to have also recreated the cars. In fact, I recently ordered many of the pieces via Bricklink to rebuild Redbeard, Kahuka and Batlord boss cars. I think you are spot on for the majority of them but there are a few errors.
1) Baron's car has a black steering wheel, not tan
2) There are too many plates on the back of Basil's car. I think you raised the car by a plate's height which is not correct.
3) Gypsy's blue seat back piece is one plate too high.
4) Kahuka's car has many minor imperfections. The spear pieces are missing two yellow 1x2 plates beneath the black clips. The grey jumper plate holding the imaginary white feater should be on top of the 1x2 grey brick, not the slope. The front section of the car is not correct. There should not be two yellow 2x2 modified axel plates although I understand why you placed them. Technically, that connection is impossible to make out of existing pieces. I would recommend having a yellow 1x4 plate followed by a red 1x4 modified plate with the two axel ends. This could be yellow too.
5) The flag hinge on Redbeard's car is a plate too high.
6) Rocket's car has black wheels.
Despite all the constructive criticism, I really appreciate the diverse models of the boss cars and yours for the most part are top-notch accurate replicas.
-MFROG5
