I've been fiddling about with the original engine, trying to determine whether its redeemable and should be reconditioned, or whether I should think about a more modern engine. I'm not ready to fully strip it down, but the fact that it seems to be very rusty on the outside, and was seized (frozen I assumed) suggested that it might take a lot of work to get it right. I cleaned the outside up a bit and it looked a bit better. There is a little bit of damage where the breather tube is meant to come out of the tappet cover, but otherwise it looks OK. After a good soak with Inox the spark plugs all freed up, and came out with the threads in the holes looking nice, so that was a bonus. I poured some runny oil (actually left over two stroke fuel) down the plug holes and watched as it poured out the exhaust manifold (Oh yeah, its a sidevalve and one of the cylinders will be on the exhaust stroke...). Then I gave the front pulley a twist by hand, not expecting anything to happen, but it freed up! The next plan is to take the head off and see how bad it looks. It would be lovely if I could get away with a light hone and some new rings, but I doubt it.