Pigdog- Nah mate they're different. The R31 insert is a larger diameter than the Stanzas. I haven't measured it but it looks to be about 2mm.
With the gland nuts if you 'face' the threaded section up to each other you can see that the new ones in the pack are larger outer diameter.
I wonder if it depends on which Stanza struts. Mine are import Stanzas so maybe the Aussie spec ones are the right size??

go to pedders, they have a book with all the insert dimentions. That way you could find an insert that is the amount you want shorter. But 50mm isnt really that much. Think thats maybe 240z ish length

R31 gland nut should be the same as stanza. They use the same size tube and generally come with fine and course thread nuts. even my camry ones came with the right nut

So how much shorter are the R31 inserts compared to Stanza?

Yes, modify the stanza gland nut to accommodate the r31 inserts

After starting my coilover coversion and strut shortening I've found that the insert retaining cap for the Stanza struts doesn't go over the top of the R31 Skyline inserts I'm using. The inserts come with two different threaded caps but neither of them fit either as they're too big for the strut tubes.
The two options are to machine out the inside of the strut nut to accomodate the larger insert or to get the strut tube slightly enlarged and re-threaded to take the strut nuts that came with the inserts.
I'm going with option A to start with as strut nuts are slightly more replaceable than struts!

3 methods for that

1. cut tube with thread off and weld that section back on after more tube is cut
2. Cute tube and tap new thread
3. heat up stub axel while cooling down shock tube to remove tube. Cut tube from bottom and reinstall into stub axel

Also, if you shortened the strut you would loose the thread on the strut tube. So how is this overcomed?

Different method of holding inser in, or do you cut and wels the strut?

Do you get a new nut or use the stock Stanza one?

Was thinking of shortening the tube by 40-50mm, so any ideas on whats suitable.

Thinging of shortening tube as using camber tops, which drop the top of the shock lower than the standard strut tops and using a SSS spring which lowered the car approx 20mm.

Therefore the standard shock is allready compressed, before its doing anything.

Thoughts?

Cheers

No, you need to get shorter inserts.
And there is a big nut at the top of the strut tube that holds the insert in

Does installing standard replacement Stanza inserts like Monroe, Pedders ect. Give you the ability to shorten the strut tube.

Or do you need to source shorter inserts?

And what holds these inserts into the strut tube?

Do they have a bolt that goes into the bottom like other inserts I have used on Toyota's

Cheers