I love vinyl. One of my fav plugs

I like the rivets.  Good reminder.  I hadn't installed the 64-bit version.
 

Apparently, duophonic was delay, hi-pass on one side and low-pass on the other, plus some stereo reverb.  I had incorrectly thought there was some comb-filtering involved, but I guess it was simpler than that.

You're not wrong.  A good explanation at the link, and a bit of a suspect pic from another source:
Using Short Delay Effects.

 
As easy and configurable as this is ITB, you have me dusting off some old hardware that excelled in 'stereo-izing'.  The Lexicon Vortex does some unique, edgy combinations with a Haas effect.  Definitely not retro.
 
But my favorite for old-school fake stereo has to be the Alesis MIDIFex 'soapbox'.  RCA jacks and all.  Mine has the Device Squard EPROM installed.  The delays, parametric EQ, and 'Ambi/Wide/XWide' options really nail it, but I think the 12K rolloff adds to the authenticity.

Danny Danzi
No problem Konrad....you should be able to nail the sound you're looking for using those methods I told you about. And...if you really want to make it cool, you can use the tape sim plug in Sonar X3 on the bus and then try this thing: http://izotope.com/products/audio/vinyl/index.asp 
 
It's free and I've used it several times for making things sound a bit more vinyl. I know you're probably not looking for anything like that, but it's still a cool plug to add to the arsenal. :) Good luck with everything man...would love to hear the track after you're done with it. :)
 
-Danny 

Do you find you have to use the DirectX version to get the warp buttons to work? 

sharke

Danny Danzi
No problem Konrad....you should be able to nail the sound you're looking for using those methods I told you about. And...if you really want to make it cool, you can use the tape sim plug in Sonar X3 on the bus and then try this thing: http://izotope.com/products/audio/vinyl/index.asp 
 
It's free and I've used it several times for making things sound a bit more vinyl. I know you're probably not looking for anything like that, but it's still a cool plug to add to the arsenal. :) Good luck with everything man...would love to hear the track after you're done with it. :)
 
-Danny 

Do you find you have to use the DirectX version to get the warp buttons to work? 

Actually Sharke, I have to use the originally released version for that. The newest one doesn't include that feature for some reason on my end. So I reverted back to the very first release which had the warp stuff in tact.
 
-Danny

Ah, they must have disabled it in later versions then. It appears to be incompatible with some hosts:
 
http://www.izotope.com/support/portal/index.php/kb/article/127-Vinyl_Warp_control_disabled

Here's an interesting article about the alleged "first stereo recording" which was "accidental" - Duke Ellington, Black And Tan Fantasy from 1932. It sure sounds great for the time. 
 
http://articles.chicagotribune.com/1985-06-30/entertainment/8502120173_1_maddening-difference-brad-kay-listening
 
And here's the recording: 
 

I tried Craig Anderton's approach to widening a mono acoustic guitar and did not like it at all. I got a much nicer result putting mono acoustic guitar tracks into a nice small convolution reverb and you could try that too. Or using the spatial enhancer below.
 
I also get good results from a free VST called SHEPPi Free Spatial Enhancer. This is of Bob Katz fame and it does some nice things to a mono source adding a sense of ambience around the track. It is easy to find and download. (32 bit I think though) SHEPPi collapses nicely into mono too.
 
The delay trick can work well too. Sometimes inverting one side might add to the effect. Another option is to create the effect (widening as per Danny say) and then run that into a stereo to M/S converter. Apply some LPF to the S signal then convert back to stereo. 
 
Here is some more info:
 
http://dallashodgson.info/articles/OpenAmbienceProject/
 
That Duke Ellington recording sounds quite amazing. It does not collapse well into mono but sounds great in stereo, very obvious.