I've been looking at an H190 head, that's a 3.8888:1 ratio. it's a steel case unit. I've got a couple of alloy heads kicking around too. They're both 4.6:1 and from C20 Vanettes. The Van diffs actually use the same piss weak little splines as the H165.
So I was thinking, if I'm able to seal the deal for this 3.88, I may transplant it's gizzards into an alloy casing. The alloy heads are crazy light. And since this 3.88 came from a C22, there's a chance it may also have the smaller splines. And if It's gotta come apart anyway, why not go the whole hog?
So, something the seller said got me wondering. Is their any compromise in strength with the alloy casing? I've only seen alloy ones in the C20's, and only heard of them on older datsuns. (411's and maybe those old 2000 roadsters?)
This will be going into a 620 wellside, with an SR20de up front.

The C22 had the larger axles common to all H190's,ie Gazelles. 720 utes, & some 910 Bluebirds. You could probably make the 3.89 fit the alloy housing, but there are probably 2 or 3 different offsets which would mean machining the carrier so they fit properly. They might even have Whitworth bolts. I had a H165 4.375:1 diff ratio imported from Japan & had to go through this to get it to fit the 4.11 housing I had. One of the axles needed to be ground down so it'd fully seat in the axle tube.
I had an alloy 4.6 ratio in a Sunny behind an A15 race motor, never a problem with the axles. There is a steel 4.11:1 ratio H190 in most C20's in Australia, the alloy 4.6 is rare as. So just a mild SR20 shouldn't worry the axles, either.
The problem with the alloy centres were they were flexing under extreme conditions, like full on 2.4 litre L20B's & FJ24's, but then again, who wouldn't. The H190 I've mentioned was originally going to be fitted behind an SR20DE'd Sunny back in 1994, but I never finished the car. When I built another Sunny up with a big HP A15, I bolted it in & have never had a problem.
Maybe you should try for the complete rearend out of a C22 Van, they're not too wide & all you'd have to do is take all the trailing arm & Panhard rod mounts off it. That 3.89 centre is probably from an auto S12 Gazelle, as the Vanettes had 4.1's for manuals & 4.4's for auto's here in Australia.

I've not crawled under it yet, but the ute already has a steel headed diff under it. Given that it was crippled by the factory fitment of a J15, it's probably low ratio (High number) as hell.
I'm still waiting for the guy to get back to me about whether or not he's accepting my offer for the 3.8888. I probably don't actually need the alloy head, but they're just so light! When I pick it up, my arsehole doesn't pucker one bit. I've also got what I think to be a 720 housing and axles here too. The splines are nice and beefy. I'm not known for being kind to my cars. So the extra reassurance is nice.
Also, another thing I've heard (While we're on the topic of diffs) is that the nissan serena vans come with an H190, and factory LSD was and option.......
So I'm told anyway. A mate bought one from a pick a part, for $50! And resold it for $650!

Nothing like a 60's Datsun 320 pickup rear end. I assume its a H190, at least thats what I label it as. A 4.88:1 and only 13 splines, the axles are beefy. It has an alloy head and they are ofcourse very light. The best think was that only minor mods to fit it under my car. Leaf springs brackets were cut off and move outward to match the car and I had to get a drive shaft build to suit the length. Spider gears were welded up. It was the perfect fit for the car.

The fairlady U20 with 150hp and reasonably heavy convertible had the Alloy H190 and used in racing with way more hp yet hold up very well. Just go for it Id say as they are build quite strong compared to the alloy h165 casing.
Ive run into 612 ute with big H190 axles with alloy centre so not all had the H165 axles and I should have taken that whole rear end but had 6 stud axles.

I'd say my 620 will have the beefier axles. (It's out at dad's block of land up country, so it's not a striaght forward thing to go look at it)
I've still not heard back from the seller yet.
It'll be really nice to get the rpms down at 100kph.

Auto Gazelle rings a bell with the 3.9 rear h190 but so does the auto bluebird S3 so you best get anything thats affordable and replace-able or easier to get for cheap yet I doubt the lightweight rears on utes are as punishing as some heavier reared sedan, coupes etc.

There is also a 3.7 from the Gazelle I think

Some s12's were H165. Or did you mean S110? (I know bugger all about them)
I like the idea of the bigger axles,as if I ever take leave of my sences and lock the diff I don't want a broken axle. Although to be fair, the only H165 sized axle I ever broke had been cut and welded. (By a pro) and that was running Pretty decent DOT drag tyres, on a HEAVILY prepped track. The same day as the comp cars were putting a lot of rubber down. So conditions were pefect. (I wasn't the only guy to snap and axle that day)
But I'm told that regular street driving on a locker will break the smallr H165 sized axles. (Hence why I don't run on in the 1200, as ute axles are too hard to find here.

S12 gazelles here all have H190 or R200 so not sure about other markets

I sold a local guy one of my spare H165's,for his S12 He advertised for an H190, but when he came to pick it up, he was like OH, thats not what I have.