QUOTE(agentblr @ Mar 15 2010, 04:55 PM)
Looking at a bare casting right now...... looks like you would run into severe clearance issues if you try to machine the plug holes on the bottom (exhaust side) of the head. The push rod tubes are right in the way! You could machine the holes in at 45 degree angle to the existing plugs(top side) but you would have relocate the CHT bung if you were using D-jet ( I assume this is not the case) I think it is totally doable. I think you will have to add material wherever you put the 2nd plug,They just did not leave much meat in these castings. I am using a 2.0 head for reference.
The heads have to be heli arc up where the plugs are going there is not enough
metal there, this will also pull the heat away. The one plug goes between the
tubes the other clears with no problems.