JFP,
Very helpful,thank you.Your experience is more valuable than my pontificating :-)
"Drilling a hole in it would be counter productive to sealing off the shaft from oil intrusion."
I was trying to address the concern expressed earlier about pressure changes in the IMS tube. AS Markus says, maybe no longer a concern.
There are brass freeze plugs listed below- easier to modify than steel.
http://freezeplugfactory.com/expansion-plug-size-chart/