Hi Keith, sorry it took me a while.
1) i realized i have two similar sets (i thought they were different ones). Both Have the part number 56105-N3785
The labels says
GS30 (Hard) 74-11 and
S30(Hard) 74-11
Both sets came from two independant european dealers (one from germany, one i found in Austria) with the set including a sheet on how to install them.
The manual seems to be generic, as it also includes instrction for the 510 and other cars:
this is the other (exactly same) set with the same sheet included, but the backside shown.
The backside is written in Japanese. and clearly shows the "AMPCO" logo, even though both sets of struts included are of "ATSUGI" brand.
That is because AMPCO = Atsugi Motor Parts Corp. So it's the same company, just different branding.
This also seems to be confirmed in this thread, with the exact same strusts and installation sheet:
Update:
Here's a closer look at the scanned installation manual. Japanese on one side and english on the other side:
If you look up the part numbers, they seem to fit for the S30. but only for the 260Z: As for up to October 1974, 56105-E4185 was used.
"OP" means "optional". This usually indicates harder "competition" suspension, or european factory specs, as we usually got from factory, what was optional competition suspension in other countries.
This information also seems to fit with the "Hard" and date indication on the box (see 2nd. picture in this post)
I still have yet to find out what to do with the two sets. Also i'm not sure yet if they're the correct euro-spec for the 240Z.
If have yet to find out if the 56105-N3785 is the 1:1 replacement unit for 56105-E4185. then it would be fitting. Otherwise it's "just" a set of (optional hard) struts for the 260Z (2+2).
So i looked it up in the parts manual. took me a while to find one where this one is listed:
So, you can see it is not listed as a direct replacement for the 240Z items. (ok that part is cut off on the right side, but it is not listed as the replacement for the up to 10-'74 items)
Means, while technically probably fitting as a replacement. they were never listed or sold from factory as an official fitting item for the 240Z.
So what do we have then?
It seems like it is a fitting replacement front shock absorber for the 01-74+ 260Z 2+2 and 11-74+ 260Z factory items.
But it's not a standard item, but
- a complete strut cartridge ("for service") to replace the original "open" style strut inserts.
- a "hard" spec, factory for european cars, or optional as "competition" items for other country cars.
You might wonder why there are so many of these struts around in europe that i was able to "accidentally" obtain two sets of them?
Well over here the 260Z never got replaced by the 280Z, so we had the 260Z for much longer, until it got replaced by the Z31.
So i guess these might be interesting for one or another 260Z (2+2) owner outside europe.
If you're interested, i once wrote a big post about the 240Z suspension and options here, but i haven't updated it in a while, so you might want to read it with a pinch of salt:
https://www.jdmjunkies.ch/wordpress/2017-01-19/240z-the-ultimate-guide-to-factory-suspension-and-options/