Got everything back together today. Eventually burst into life, after a bit of juggling with throttle and choke settings. The engine runs well and fairly quiet for a two stroke. It doesn't rev hard, which is just as well. You'd never hold it.
It did keep throwing the drive belt off. This was down to the pulleys being out of line. I found the brackets attaching frame to motor/drive unit slightly bent. Holding the engine down with one hand and levering gently on a length of wood, inserted between the frame tubes, things lined up and the belt stayed put.
One thing I didn't bargain for, was the throttle cable parting company with the carb' slide. I must ave pressed the throttle lever a little to hard and the nipple on the slide end came off. Now the nipple is just a small, read minute, lump of solder. Had a happy time re-doing that. Got there in the end and I will be more gentle with the throttle lever in future.
Had a test trial on an over grown hedge down the lane. This showed up three things. One is the blades could do with a sharpen. The second is it's a heavy beast. I wouldn't want to have to use it for a long time. The third is make sure it has enough petrol in the tank.
I'll get the blades sharpened, give it a clean up and leave as is I think. It will get occasional use no doubt. But I think it will mainly be an exhibit at shows etc.