Yep, fitted the new GM spark plugs which are actually NGK R plugs this afternoon. Got the dist pack out fine as well, made it a lot easier by threading some bolts into the holes where it screws to the head, and used them to pull it out.
Also, the 4th plug from the cam belt side, found out that it had got the rubber from the spark plug socket melted to it, which explains why it was difficult to get the dist pack back on last time!