Guys,
Educate a non-machinist a little bit. Since that spigot just hangs down there (I'm assuming here) why would it have to be precise? Couldn't you just grind it down with anything and dress out the burrs with a fine file and be good to go? As long as it isn't touching anything seems to me that precision wouldn't matter.
Never too old to learn,
Leonard
Leonard,
It needs to fill the recess in the head for the proper compression sealing, as Will mentioned.
Even if it is not quite touching, we want it to be as close as we can get it.
So, a typical method is to take off the head and previous gasket, and then put the head back on without the gasket(no torquing for this check), and use automotive-style feeler gauges to measure the gap where the head gasket goes.
If it's even all the way around, then you only need to grind down the spigot evenly all around. If not, you need to address the uneven issues too.
But, when you get it done, you want it to have a feeler-gauge gap of half the thickness of your head gasket.
That way, when you torque it down, and compress the head gasket, then it will be right, and the head gasket will be compressed enough to seal the pushrod tubes.
It's a matter of getting 2 different surface planes to be in correct positions to seal 2 different things when you torque it down.
If you lap the head to eliminate the gasket, then you just grind the spigot until the head sits right on the barrel evenly, with no gap at all.