I bought a 1650 aluminum boat with a 1990 dt30 on it that had “low compression”. I checked compression after getting it home and it had 120psi on 2 cylinders and 115 psi on the third. They tried to remove the thermostat cover and broke the bolts off so I thought I’d just order a new head cover and then.... I broke a head bolt. So I now have the power head off and I’m going to take it to a machine shop to get the bolts removed. I would like to get a little more power out of it (shaving the head, lightening flywheel, Boyeson reeds, etc) but is it even worth it? And if so, how much can I safely mill the head?