I think its a block plug, this one in particular is on the driver side head, but they are located on the sides of the block too. My machine shop forgot to replace one they removed from the passenger side of the engine by the KS. What is it... where do I get it... and what size do I need 3/8 what pitch...

 

I would just take one out and bring it to a plumbing supply store to match.

 

Looks like a socket set screw. Hard to tell from the pic and the paint. If it is socket set screw then any fastener place should have it. Give your machine shop a call. They might know the size and have some laying around.

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Looks like the pipe plug used to fill the hole that the steam tube would bolt to, if the head was reversed and that end was in the back. Find the threads for the steam pipe bolts, and you will have the threads for the pipe plug (NPT threads?)

 

Looks like it's GM part #144011, but the part is discontinued(imagine that....grrrr).

The part description is as follows....

PLUG-SQ SOC, 1/4-18X.44 AM STD PIPE THD, STL, CZ(CYL HD CORE HOLE)

Number required.....2.

 

awesome, yeah... if i reversed the heads the steam banjos would be here. The machine shop left one out near the passenger side knock mod, and i fear coolant will flow if i don't plug it back up. I wonder if i can reuse one if i pull it off a junk lt1 in a yard...
thanks!!!

 

That should work, just be sure to use a high temp thread sealant on the threads.

 

You can actually just go to Ace hardware and get a 1/4 allen head pipe plug. Put a little teflon thread sealer on it and your in business.