above deck ?

Using the OP's flat top pistons and a closed chamber heads I could see going through the process of building a quench motor. With an open chamber and a flat top piston the squish to the exhaust valve just isn't there. I'm not a pro engine builder but have built a few in my day and this is my opinion of why you need a closed chamber for a quench motor.

read this article
https://www.rbracing-rsr.com/squishcalc1.html