A LSD diff that bolts into the housing for your wagon is not that hard to find, the down side is plan on paying $1200-$1500 for one. I found a deal on one for the 1200 coupe I race and it was still $1200. You can try roadster sites like 311s.org etc. there's lots of info on the net about swapping side gear on the truck diff.
I'd strongly encourage you to do you're research. The prices for the 23 spline diffs are getting steep and replacement parts getting scarce. If you have acces to a diff shop that does work for reasonable prices (read takes pity on poor Datsun guys) than having the truck axles redrilled for the bolt pattern you need may be an option.
The days of $600 units are gone..........sigh.
I've been hunting for a way to avoid needing to find a competition roadster diff. I think the truck axles sound interesting, just concerned about what gears I could find and what the actual LSD's break away point it like. I autocross, so I'd like it to actually be kind of low, probably lower than what the trucks were built with.
I'm looking -- at the same time as searching for a Nissan unit -- at other options like RX7 axles (first gen GSL-E) and Corolla GTS units (AE86). Both of those have more "reliable" availability since you can search for specific years and trims to get the axles. Downside is they're both small, I believe the Mazda is a 7" housing and the Toyota is a 6.75" or something like that.
While I only make about 140hp right now, I'm probably going to three link this axle once I find it and so I would like the unit to be strong enough to take around 250-300hp, if I ever feel like getting there. However, anything American or the H-233 (I suspect) will be HEAVY, which I would really like to avoid -- add lightness and all that.