somebody might have already done this, but i thought i would show how i plugged the head after removing the air injection tubes on my 300.


you need six 9/16 fine thread bolts, length isn't too important, i got 1 1/2's.


i used a vise to hold the bolt, and a hacksaw to cut the slot, i tried using a cut off wheel and my sawzall, but the hacksaw did the best job


cut off the end so your "plug" is only 1/2" long, i tried using the chop saw(was ok) and sawzall(sucked) but my 4 1/2" grinder with a cut off wheel did the cleanest job. I clamped the bolt in the vise to i could run the wheel across the top and get the right length.

i cleaned up the threads on the end a little with a thread file and installed with a standard screwdriver, I used a little loc-tite on them, since i dont plan on removing them. but after installing them, i don't think its neccessary, they fit in there pretty snug.

 

If I remember right those smog ports are pipe thread.
You can buy both 9/16 UNF plugs as well as 9/16 NPT plugs from most large hardware stores.

Nice job though.

 

i thought that they were, but was proven differently. and I wasn't able to find and plugs in fine thread- even at fastenal.