As part of going back to the factory air cleaner, I need to remove two nuts on the head studs, position the air cleaner bracket, and re-torque the nuts to 53 lb-ft.
Do I need to loosen all the nuts on the head studs to avoid warping the head?
Is there any risk of messing up the head gasket by loosening then re-tightening the nuts on the head studs?

 

No ~ only loosen the 2 required nuts to mount the bracket for the aircleaner. Did it myself on my car to paint the bracket as the powder coating did not like the heat & started lifting. Zero issues. Do it all in one session with a cold engine.

You have a nut between the 2 mounting points. It's safe. Make sure you get the correct Brass wingnuts to attach the aircleaner body. Looks & is correct. Well they are a sort of silvery brass/bronze. As long as they are wing nuts. And no they don't come lose. There is a plain washer under the wing nuts.

 

I endorse Glyn's instructions.
I did this myself about a month ago when I changed my MK2's old "pancake" filter system to the later drum system.

 

Thanks for the endorsement Bill. I understand Thorsen's trepidation.

 

I've done it as well to add a bracket for a coilpack. No issues with leakage etc.

 

At the end of the day this was a moot question. The air intake I bought was promised to fit a 420, but they must have meant that in the theoretical sense of "anything will fit if you have a grinder and a welder". I put the gasket for the air cleaner on top of the manifold and you can see this intake was made for something with smaller carbs. Or someone put bigger carbs on my engine. My carb throats measure 2" and the intake holes are about 1.61"

 

I think the gasket is for the HD8 SU's.
The HD6 carbs, are 1-3/4 without checking.

I believe that you should say plenum chamber, the manifold bolts up to the head and is in-between the head and the carbs.

 

I think the 420 did get 2" carbs, whereas the S Type was 1.75". I suspect you have an S Type plenum, not 420.

 

You definitely have the wrong plenum for a 420.
What you have is the plenum for 1&3/4-inch carbies and it was used on some MK2s as well as 240,340 and S types which had the "drum" transverse air cleaner.
Just for info there is also a different plenum used on MK2s which have a pancake air filter
The 420 used 2 inch carbies and I have one of those plenums in my possession. How it got there I don't know, suspect FOT (fell off a truck) as i have never owned a 420
Unfortunately, some ambitious person in the past polished the whole thing and managed to eradicate the part number so I can't help you with that.
cheers

 

Part number for the 420 air intake is C26961 where as the part number for the S Type and Mk2 3.8/3.4 340 is C15554. The 240 part number was C27828

The part number on the air in take in the picture is C12584 which when put into Google does come back as the air in take for the S Type and Mk2 but this is only people who are selling it and might not know what they have got. C12584 actually relates to the Mk1 2.4 and was fitted to early cars but was later changed to C15554 on later cars.