D ,I think the sigma and starion have the same diff centre and irs. Funny you mentioned alfa cause I remember in the 80's a few people that rallied 1200's and 1600's used alfa and fiat irs diffs with lsd and disc brakes etc. I know the fiat is a very light and tough diff as I ran 1 in my 1600 but it wasnt irs.

Live axle -
Borgies although have their place they`re quite heavy for lightweight datsuns yet most of the time theres no other choice. Unless you have a h165 with lsd or h190 lsd with alloy carrier.

The price of Winters and similar Quickchange rear ends using conventional gearsets to rid the noise makes them a better option than off the shelf borgy setups some sell for a high premium.

For IRS there are heaps of option although all require lots of work.
Although the DeDion is not a full IRS its still amazing in Alfas, Volvos and many others yet so far its the easiest for me to attain.
As the Volvos 360 are not Volvos but DAF designs they bought out, DAF had cars with leaf sprung rear ends which then incorporated the dedion design using the original leaf mounting points to save money.

If the Sigma irs centre is like the Starion irs centre then they can handle alot of abuse especially since there have been plenty of 400+hp starion turbo 4g63.

Borgwarner diffs are proven n tested, they still use them in v8 Holden comodores, I dont see sigma or that 8 inch thing your referring to in anything that's got power, borgies can handle a fair bit of punishment n a lot of horse power

Also unless your running a v8 wiith decent power a 9 inch is the worst thing you can so to it, a 4:1:1 28 spline or 32spline with minispool diff is the way to go

Starion like IRS you referring to yes? well thats the only one I can think of as I havent seen the sigma IRS but also theres an evo all alloy torque sensing irs diff.

Either way the closest independent rear end we can go without too much fussing around is use the mono leaf springs, torsion beam and CVs and hubs from a volvo 360, a couple of pipes to attach from chassis rails to hold the irs diff, modded drive flanges to suit the volvo CVs or mod your choice of commonly attainable CVs and your choice of shockers or coilovers but latter no necessary as mono leaf volvo ones are bulletproof.

This is the way Im going but still deciding on whether to use a suzuki grand vitara, mitsu evo or other alloy cased irs lsd unit.

Hey D, is it a big job to go independent rear end.. say off a sigma ??

Earlier Volvo diffs are an option too as they used Dana diffs and Jeep components can then be used,Volvo axles were rated for use with steel snow paddles so they are tough as well.When you look at all the vehicles running Dana 30 diffs like the Volvos there are a good range of ratios available.
But when it is all said and done the Works Stanzas initially ran Alloy Centres but went back to Cast Steel housings due to reliability issues with the housing getting hot and bearings coming loose in the alloy with anything over 200HP motors.

True the days are gone for cheap lsd live axles hence Im hoping I can do mod a volvo 360 de dion conversion and use either subey, miata or suzuki lsd. Nissan r200 is too heavy

http://datsun1200.com/modules/myalbum/photo.php?lid=22998

We also have a place in the northwest that does up RX7 GSL-SE units to fit Roadsters for about 1K. You supply the axle, throw in shipping and price for the Mazda axle price likely to be $1500-2000 which considering all that needs to be done is a good price. Just not cheap. The days of buying a complete unit for $500 are definitely gone.................keep in mind I bought my H145 LSD 15 years ago and just assumed they were still only $600-700 for a LSD unit, like they are on newer cars.


Tom

RT- for the 8 inch the viscous centre I listed is 524usd and ally carrier 330 or so, then if you use their services they can shorten the housing you supply for around 280, axles custom are 150 each so its looks better than h190 as the R&P new are 190-220 each also for your choice of ratios.

Just as an FYI, as is obvious from my H190 post, I've been checking all the options. To get a custom complete rear axle will set you back between $2300-2600. That is everything axle tube, axles LSD diff and brakes. You could pick up some parts used and possible shave this down a bit.....................but I still think the minimum is 2K. If I get lucky I may have my H190 completed for $1500, and that is with selling off the extra bits from the parts car the housing came out off. There doesn't appear to be many cheap options left.

Tom