Most all manufacturers of gas valves have a pressure drop of one inch wg
you mean a valve cover gasket i think
10 foot pounds
The first thing that comes to mind is a blocked PCV valve or the line going to the PCV valve.
look along the valve covers on the heads, there should be a small pipe that when pulled seems to go no where, that should be the PVC, it is a simple fix
All the way. It may be dangerous to throttle your gas flow down using the tank valve.
$32.75 from autozone for a twin cam
In 2012 about $40
It should be between $17-$24.
If you do not feel comfortable doing it yourself, ask a plumber or HVAC tech. It is not an expensive or difficult fix. Price of the valve and a service call should cover it. Shut the boiler down a few hours before he comes to allow it to cool a bit before he drains it will help.
Depends which species. Usually the size of its eyes.
between 250 and 400
If you are not sure where the heads are I wouldn't try to get to them. Generally speaking though the heads are underneath the valve cover which should be very easy to spot and generally is only a few bolts. But be careful because once you take that valve cover off you are in dangerous territory, if you scratch up a head or drop shavings in it or pretty much do anything to it you can seriously damage or destroy an engine.