Why not have the original motoplat rebuilt?
I'm a bit on Lozzas team here...the Motoplat was never a great ignition in the first place when compared to even the very early Japanese CDI ignitions. I've had a brand new off the shelf Motoplat last one ride and have spent good money having it and other Motoplats fixed. They work OK but you never know when they're going to fail. I've been using PVL ignitions on my Maicos for over 10 years and have never had one inkling of a problem with them....never touched 'em once I fitted them. It's the same with the CDI ignitions on my Yamahas. I've been using MX250 inner rotor and DT400 outer rotor ignitions on my DT1 based specials since day one of VMX with zero failures. In all of my years of racing the only ignition failures I can recall have been with Motoplat or Femsa.
Now we're in the new millenium, why not use new millenium electronics to keep our old bikes user friendly?
There are some good kits coming out of the UK based on model aeroplane ignition, there are other kits out of Czecho, Slovenia and even China that are infinitely better than a 30 year old Motoplat or even a brand new overpriced PVL. You'll find that these modern ignitions are often cheaper than having your Motoplat rebuilt. You could even modify any number of rock solid Japanese ignitions to the Kato with good results.