The fittings aren't in the exhaust manifold, they're in the head itself. They're M14x1.25 thread. Oil drain plugs far various vehicles are this thread pitch but you may have trouble with sealing, the original fitting seals on a lip at the bottom end not at the tapered seat in the head. You can also use the threaded portion of the original tube fitting for a plug- cut each tube & remove, tap & thread the inside of the fitting with the proper size bolt as a plug (or solder/weld/braze the hole). This method has the added benefit of the fitting being the proper length so that there's no "chirping" that sometimes happens with a shorter plug. FYI the EGR bung in the exhaust manifold is M22x1.5 pitch should you also wish to plug that. The original threaded fitting with a 1/8" pipe plug in place of the tube is one way.
_________________ '78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, rough body, bought new 12/4/78. '87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch,more to come.
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