Finished! Brutal 'Cuda

I painted my whole car first... Worst decision of my life... If it was me I would primer the engine bay/interior or whole car. Then begin to build/mock up the drivetrain and interior. That way if you have to cut/drill/grind you don't lose ground and have to repaint anything. Once everything is ironed out then I would take it apart, send either the interior/engine bay for paint (or the whole thing for paint) and rebuild it. Then paint the exterior.