The engine head has been modified a couple of times already. I have lowered it 1.2mm in total and it had already been lowered. I don't know how much tough
Intake and exhaustports have been made larger and polished. Better flowing 38mm stainless steel intake valves were installed and combustion chambers were modified a bit. Also the valve holes in pistons had to be enlarged.
Now the compression rate is around 10-10.5:1. It could be higher but I don't want to blow a gasket every week.
I think it would be better to raise the compression rate rather with better pistons than lowering the aluminium engine head. Camshaft is modified apparently from an original cam by welding and re-shaping it. It has 10.3mm lift and 290-295 degrees. Looks pretty roughly made but works. It also has an adjustable cam gear.