Thread type/ pitch help

I am having problems
Finding the type of threads and pitch on the two holes in the exhaust manifold on my 258 inline.
My goal is to block them off with plugs

 

those may be a thread that dosnt match up to any plug i usually find a pipe plug that sorta fits and weld em.

 

Could be metric threads.

 

I had to buy mine online for the 304 manifolds. Unfortunately I don't remember the thread pitch. I highly doubt it's metric though, I know mine were not.

 

The hole to the right normally accommodates the EGR tube, connecting to the intake manifold. It can also be plugged, on vehicles with no EGR. The plug is a Jeep PN J0639979, and appears to translate to Willys era PN 639979, a Jeep 4 cylinder oil drain plug. http://www.jeep4x4center.com/oildrain-plug-4-cyl-639979.html So you may have lucked out with that one.

The center location is plugged on my manifold (my upgrade to the J10), though it may accommodate an exhaust gas oxygen sensor. The plug is Jeep PN J4200413 - which brings up http://www.partswebsite.com/dcjparts/oemparts/4200413.html - as I suspected, it's the right size for an oxygen sensor. You should be able to find a plug lots of places.

 

The ones in my doug thorleys are fine thread. 1/2? 7/16? 9/16? Somethong like that. I have a thread cleaning set i got at sears i use all the time for this stuff.

 

I have also plugged the air injection ports, which should be the same as a V8. Advice for the V8 won't help with these ports. This is a 6-cylinder manifold.

 

Here is the route I took when plugging the air injection holes
http://www.earlycj5.net/forums/showthread.php?70430-Need-to-plug-a-hole

 

Thanks Tim!