I agree, I would replace pretty much everything but the crankcase. Then again, seeing as how not much money is tied up in this engine you might be better off looking for another. You could probably buy a whole Brumby/Leone, take the engine out and sell off the rest as spares and maybe pay for the engine.
As an interesting aside - BMW used to base their 1.5 litre F1 turbo engines on blocks out of BMW 2000 model cars that had done quite high mileage. Apparently the idea was if it hasn't brkoen by now it never will :) If anyone is interested I can dig out the article and scan it.