where you say
I've bought a ignition system from the local wrecker off a early 80s YZ80
i'm guessing you've got the stator,flywheel & cdi box? from a YZ80.
i'd be looking for something with a little more flywheel weight {1550~ish grams=perfect} aiming for "torque" instead of revs.
early DT's, really are a good choice for the DT/RT1 motors as they bolt straight in.
if you proceed with the YZ80 set~up,
you'll need a lathe or someone that can drive one.
fit the stator plate first {you may need to machine up an adapter plate},
then you'll know what needs to be machined off the flywheel to make it fit.
it's a bit of rooting around but can be a heap cheaper than a PVL by comparison.