Andy,
A notch feel is indicative of rollers that have developed flats. Usually from overheating due to lack of oil or insufficient radial clearance. It is not uncommon for the outer race to spin in the connecting rod. Alls sorts of bodges have been seen to try and secure them - punch marks, Loctite, tack welds - but the main problem is insufficient meat to back up the race and the eye stretches and the press fit becomes slack.
I have not had the oil gallery plugs out of an EW crank, but if they are designed like the OHV cranks the the plugs are threaded in until tight and filed flush. I remove them by taking a small steel machine screw nut, centering it over the plug, and welding it through the center hole. Then you have something to get a purchase on to wind them out. They are usually not very tight, especially after the weld cools and contracts.
This will be the opposite impression you will get if you try to drill the center of the plug and tap in an 'easy-out' device. You will wonder how they could ever possibly got the plugs in so tight, but it is the 'easy-out' expanding the plug and making grip the tapped hole incredibly tight. I know, I tried it.
Before thinking of welding on the nut I first tried building up a column of weld on the center of the plug. With patience and a steady hand this will work but it can be a bit of a bother getting a grip on the blog of weld with the pliers. Also if you stray off the center and weld the plug to the surrounding crankshaft you will have even more trouble getting the plug out! Using the hole in the center of the nut as a fence helps prevent that and keeps the weld in the middle of the head of the plug where it belongs, and it is about a hundred times faster. Countersinking the nut a little so you can get the welding electrode closer to the plug is an advantage. It does not take much of a tack weld, but if it does break off you can always get another nut and try again. I used a TIG torch to weld the nut to the plug, and I think it offers the best control to avoid going too far. But I suppose a MIG weld might work also. I would not attempt it with traditional 'stick' electric welding.
You will need to make new plugs, of course. For comparison the plugs on the DT crankshafts are threaded 3/16-27.
Doug