I recently changed all of the coolant hoses on my ‘72 E, s3. In the course of the process I found an oil leak (no big) at the front of both sides of engine at head. These six nuts were not tight… in fact tow we’re not even snugged down. So I went to my handy ROM (Repair Operation Manual) which identified these to be tightened LAST in the torque process. Here is my question… WHAT IS THE TORQUE SPEC FOR THESE SIX NUT? the ROM simply identifies the head bolts/nuts as either 3/8” or 7/16”. These nuts are 1/2” nuts so hence my question. I have included a pic from my ROM for clarification. Thanks for a bit of attention!

 

Your picture seems to be showing one of the cam chambers. I see the cam in the centre, but the XK engine is a twin cam engine ! So I have to say, I's not clear what nuts you're talking about. However, based on my own experience, the main head bolts with nuts are the large chrome-topped nuts between the cam covers, and at the front of the head, there are six, (I think it's six) smaller studs and nuts to clamp the head gasket where the timing chain chamber is. - 2 each side underneath, and two on top at the very front of the cylinder head.
The head is not just clamped down to the block with the large head studs, but with smaller diameter studs, to the timing case cover, but of the four on the underside, two clamp to the block and two to the timing cover, as do the ones on the front.

Sorry, But its a very long time since I assembled an XK engine so memory fades on, and I may not be totally accurate.

A photo would help. On very early XK engines, these smaller studs and nuts were not present, and jaguar found the engine leaked oil there, so a quick redesign took place to provide some clamping pressure.

Edit
Sorry, but just remembered something else. When Jaguar faced off the deck of the block, it had to be done with the timing cover in place to give a totally flat area for the head gasket to seat on. So if the engine is dissembled, and the block faced off again, the timing cover must again be bolted into position when doing so. If not, then there is the distinct possibility of a step between timing cover face and block face, thus compromising the head gasket clamping at the front of the engine.

 

 

The torque specification for Jaguar XK engine cam bearing caps (including those in the XKE) is 12–15 lb-ft, equivalent to 132–180 inch-lbs.
Not sure which nuts you are asking about
Rgds
David