Removing the cylinder head, cylinder and exposing the piston

This morning I took off the cylinder head. After scrubbing off thick carbon deposits I exposed the writing on it. It says 90 SS (which I assume is the cylinder from a Vespa SS90, which is good)

The engine, sitting in the middle of my front room

The cylinder, still intact

The cylinder head, after removal and scrubbing

The piston head, still in the cylinder, covered incarbon and other crud

The piston, once the cylinder head has been removed

Now I've had quite a lot of problems with removing the ~30 years of grime coaating this engine. I've been recommended using:
1. Household oven cleaner, which I tried. As it was water based, it made the exposed metalwork rust. not good.
2. WD40, which I tried. Though there's no rust, it sticks to the engine and doesnt wash the crud away.
3. Petrol, which I'm tring at the moment. Seems most effective actually. The combination of a petrol bath, a wire brush and a toothbrush for finer detail work seems to remove the most crud so far, but it is by no means perfect. My cylinder is still covered in crap.

The cylinder in a bucket of petrol, with a toothbrush sticking out of it