Lowering/resurfacing 2 stroke cylinder deck, and cutting the new o ring groove

I've done this job so i can try differents combustions chambers that i've already machined and tried on others configurations, without the need to machine a recess in each head.
Most of the time i do my test on cylinder that don't need this type of work, or a recess in the head, this is a cylinder that i had and i decided to try something new with it. Of course between the cylinder and the case there is a spacer to bring the timing around an accettable range, then i fine tuned the degrees etc