For block pressure, tap into one of the pipe plugs near the front of the intake manifold near the thermostat housing. Not the best pic but this is on my old boat. You can see the guage to the right of the thermo housing. On my new boat I ran a braided line from the manifold to the dash and have a guage in the dash.
http://www.***boat.com/image_center/...w_Pics_001.jpg