in the old Land Rover I just got the drill and drilled a hole in it and popped it out with a screwdriver, you should probobly not do this on the skyline as metal shavings could get in the engine, but if worst comes to worst.
Putting them back in was a bitch, make sure that you get areas very clean from rust and grease. I used some Extreme Temp gasket goo and applied to to both the Block and the Welsh Plug, waited till thay bacame "tacky" and then tapped them into place with a similar sized socket.
I am not saying that this is the correct way, but it worked for me and got me out of trouble (I was actually 200 Kms from home when this happened).
Chris
ps... Make sure that you get Brass Welsh Plugs.