"It is such a PITA to get car seats in and out of my 40, I know it'll be easier with a 4 door"

May I suggest a solution that will save you at least $100,000......buy another set of child seats and leave them in whatever vehicle that you think is a pain to remove child seats from.....never bought kids seats but they gotta cost less than $300 each for a decent one. Assuming it costs a minimum of $100,000 to build a nice car, this saves you a lot of coin. Then, you have more time to finish a project.