A family of different platforms
MR-03 and MR-04 identify Kyosho rear-wheel-drive platforms, not every 1/28 car. Kyosho AWD, FWD and Buggy platforms use different drivetrains. Independent chassis from PN Racing, GL Racing, Atomic and Reflex Racing have their own parts and electronics requirements. Shared scale does not mean shared fitment.
Body fit is a system
Common Mini-Z on-road wheelbases include 90, 94, 98 and 102 mm, with other lengths on particular models. Match wheelbase, front width, wheel offset, body mount and tyre clearance together. MM, RM and LM describe motor-mount configurations; do not assume a mount change will work with the existing body or differential.
Follow the load path
On a traditional RWD Mini-Z, the rear motor pod moves relative to the chassis through a T-plate and damping system. The front end controls how the tyres meet the track. Check free motion and symmetry before tuning spring rates or geometry. MR-04 components are not universally interchangeable with MR-03 parts: confirm part numbers and the exact generation.
Check the manual and fitment chart before ordering a part.