Sorry, Pops, the only compression release I'm familiar with is the systems used on B&S engines, which is automatic and not what you want. Your intent is to be able to shut down the engine normally, glide around awhile with the prop stopped (due to compression), then restart by releasing compression so you can get starting RPM (so, no need for a starter and electrical system). Right? Your idea of an actuating rod through each valve cover, with cams to hold the exhaust valve (rocker) open slightly (could be twist or push-pull) sounds fine. It does complicate valve cover removal (I seem to open mine up often). I'd probably consider the pro/con of this idea vs adding a starter (without an alternator, just a larger lightweight battery good for a few starts).