Ditto what JC has said.
when doing something like this it's important to get the terminology right.
a budget replica for me would be the
DT2,3 engine into a,
{modified engine bracket} DTa frame,
with the best YZa type suspension/wheels you can get your hands on fitted with the YZa tank,
MX seat etc
ignition,pipe,ported DT2/3 barrel,MXa/b or even earlier gearsets will interchange without too much drama
and you're away.
the YZa clutch,flywheel & sprocket covers will fit the DT/RT1,2,3 motor but not the DT/MXa series.
or,
just throw a YZa tank onto an MX250.