The DEF is for M48A3s. The Dragon part with the ribs on the doors part 36, while included in several kits, is only for M48A3 MOD Bs and M48A5s. The part is not that hard to convert for use with the M48A3 and Magach 3, but it's easier to use the DEF parts. Yes the part for A2s and Magach 2s is different from A3s.
M48A3 MOD B, same on the A5
Why would they change the engine doors on Magachs? It's what ever they were based off of.