Using one of these in a software environment is great compared to an actual rack unit. I have one that a friend wanted me to work on. It's actually a "Red Stripe" clone of an LA2A that I'm retro fitting with  vintage UTC transformers. The clone isn't a dead knock off and the original, vintage, transformers are slightly different than the ones in the clone.
 
What really surprised me was how simple the compressor circuit is, and how much people pay to get one. You can buy up all the parts for about $500. The rack case and the transformers are the most expensive components. The other thing that I found interesting is that the clone maker used carbon resistors and cheap caps. A bunch of background noise could be eliminated if you upgraded the signal path components.
 
At any rate, I'll have a very good understanding of where the magic comes from, by the time I've finished this project.

I know this puts me in the heretic camp... I used to repair studio gear, and more than a couple Urei compressors crossed my workbench. If asked I would 'upgrade' the passive components, and yes, the noise floor dropped measurably.
 
Even so, I have never been a big fan of the LA-2, or LA-3 for that matter. I do like the LA-4, and I love the 1176, but maybe I just never learned the secret handshake, the LA-2 and LA-3 didn't work for me.

Still, I will be very interested to hear what you uncover...

You can buy kits for the LA2A and 1176 and they are reasonable.  I don't know about the components, but many if not most of use are not up to the assembling and soldering w/o spending an inordinate amount of time.  You boys can probably do it all quickly, but $500 would be the cheap part for me putting one together.  and then having to redo everything since I screwed it up somewhere.
 
The Warm Audio 76 is a good facsimile and has that sound we've all heard.  It retails for $600, so the $100 saves me a month of grief.   I don't know if it is exactly the same, but it is close enough for my ears.  And others, even the pros.
 
Do let us know, Amp, about the magic.
 
@

I love my LA-2A sims - I have modeled versions from 4 companies. :P
 
-Ki
Salem Beats

So far the only thing I've learned is that it must be very difficult to do a stereo master using the vintage units. There are a lot of sources of variation in the real deal. Transformers on the input and output will be slightly different and the internal components are highly variable. The optical modules could get real sketchy. They just didn't have the precision back then, so using 2 comp units has to result in differences between left and right channels.
 
I have little experience but feel confident that an engineer could easily find their favourite comp in a pile of them. They could also identify a unit that they want to avoid using.
 
We are so lucky using the software versions because we can use them at will, with confidence that we know how they will respond. I really like the sound of the LA2A but I'd trade the tone for consistency and ease of use.

Software is good and that is a good point about stereo use.  I suppose modern versions would be easier to match - vintage units, who knows.  One of the retailers sales the WA 76 w/ a stereo insert for two units.  I'm not sure that I want a '76 stereo unit, tho, esp. for mastering.  But I do know the sound I squeeze out of the WA 76 is much better than any software I've used - Cakewalk, softube, etc.  A couple of pieces of good analog used going in can get that big studio sound, while the software adds polish during the mix.  The opposite ain't always true.  I guess I should say good analog going in makes getting a pro sound easier.
 
@

AT
 The opposite ain't always true. 

That's wisdom right there!