yep, key stock, or you might try different allen keys (hex keys, what ever you call them in your neck of the woods). not the best idea if it has a lot of torque on it, but it might work...

 

5/16 Square drive is what it takes.

 

got it removed ?

 

They're called Pipe Plug Sockets-

SK Pipe Plug Sockets and Pipe Plug Socket Sets

 

No, I hear they can be stuck in pretty good. I'm gonna track down a tool vendor and buy a proper tool, as I've been a tool and may make the same mistake again. Sad thing is, I asked my machinist about this when I had the heads serviced and he said it did not matter. I called him after I realized I put them on the opposite side. I rebuilt my first 98 4.3 for my girlfriend. I still have not gone back to that one to put the valve covers on the right side. The oil fill is on the drivers side and it is deforming the intake tube a bit. I'm a tool but I'm learning.

Thanks for that pipe plug link. That's decent price too. My luck I'll break the thing.

 

This is the 5/16th pipe plug socket I borrowed. Thanks to everyone. http://i1137.photobucket.com/albums/...1999/002-3.jpg