Straight above the pad on my Dart Big M tall decks there is a removable 3/4" bung that appears to go into an oil gallery.Can anybody tell me what is?Can i mount a oil temp sensor there? Thanks

You mean a 3/4 npt pipe plug. Remove it install a 3/4 reducing bushing to a 1/2" or 3/8" what ever the size of the temp sender is.

Thanks.I've fitted the sender there.Is that gallery,before the filter/cooler of after.Need to know what i'm measuring.Yes it's a NPT plug.