Yep the early units used the 4 spider gears and a double splined drive shaft. These are much stronger than the ver 2 which is basically an open diff with the viscous unit. There are a lot of open diffs being sold as vSLD as the ver 2 and open look similar however the bar between the spider gears is different and the extra thin bolted on side plate. The ver 1 is very different looking and closer to the CLSD in appearance. Its all written up on my R160 conversion guide. Brave to take apart a suretrac unit as they are a PITA to reassemble!

Early and late diffs do actually use different sizes crown wheels bolts actually.   Yep in fact I think the R200 have them too. Obviously the R180 units don’t fit in the R160.

So did the AP come in R160 and R180 ?

But of course the suretrac can be mated with any ratio . I think I still have a Subaru Suretrac unit in my shed . I run a 4.11 ratio diff . There were also two versions of the viscous Subaru units . One standard diff with a thin viscous unit and two Spider gears and one stronger diff with a thicker viscous unit and four spider gears . 

Thankfully with making the conversion kits for years I have a few suretrac’s on the shelf though they are always in 4.11. 

You were very lucky to find an AP Suretrac . Very rare . An amazing piece of engineering . I have some pics on my phone . I’ll post a couple if I can find them .

Small update, i have built a hybrid R160 rear diff up. Using a 3.54 open diff and a 4.111 apsuretrac to give me a cheapish good ratio torsan diff. They are fairly bullet proof and wont suffer from the same  issues as the viscous LSD's of the fluid aging.~ Though probably should have baked and painted the casing before assembly 

Ok they arrived today which was superfast. First impressions are that they feel super light and well made. Over 1kg per side saving which is a huge plus on unsprung weight. I have compared them to a spare Gt6 hub. (I removed the bearings and races and stubs though a small amount of grease remained. The inportant bearing dimentions are identical so big win there as well as a 1.1kg saving per side. However the bolt holes for the disc are not taped like they on on the cast iron one and the stub holes have no groove marks in (though i guess with it being ally once they are pressed in they will form their own. The centre of the hub also doesnt have the same big void the stock one has. The rear of the hub doesnt have the same external step in however i cant think why that would mater.

Can't you just cut 3inches off the long one?