bitflipper
Cool. You not only got the harmonies and phrasing right (it'd be tempting to elaborate on the original) and you even duplicated the reverb. Don't be afraid to flesh it out with some synths, percussion or orchestration. The picked guitar should work to generate a tempo map using AudioSnap, and then you'd have a framework for layering synths and sample libraries.

Would you be able to share how this might work?  Or indeed if it would work if the tempo does vary?
 
As I said, I didn't follow a metronome when recording this originally so it is very likely the tempo isn't constant throughout the recording.
 
Just that I don't have a hardware midi input I can use, so it may be tricky to do.  But I am willing to incorporate some extra elements into the recording if I can make it work.
 
Thanks all for the kind words.  Getting the harmonies as right as they are (and I know they're still not perfect) took more takes than I care to remember!  Quite a few of the recorded tracks ended up with me swearing loudly when I hit a complete bum note. 

Alex von Elzer
Nice. I love the guitar sound. So bright and crisp.
Thanks for sharing

The guitar sound was produced through my old Zoom effects pedal using my favourite clean preset I've set up on it, with further reverb added through a plugin on Sonar and some EQ done on it.
 
It definitely sounds nicer than the original mix I uploaded.  I think the EQ took some harshness off of the audio, and I prefer the reverb I've used for it on Sonar (this was recorded in Studio One before I'd started with Sonar, but the mix I've uploaded was done by importing the tracks into Sonar).

Very nice job, but I missed the drums.

philz
Very nice job, but I missed the drums.

So did everyone else

 Nicely sung. I really like your voice. Harmonies are good. Guitar is pleasant and clean. Like others, would like more instrumentation. 

Kevin,
This reminds me of the original version of SOS on the first S&G album Wed Morning @ 3 AM:
https://www.youtube.com/watch?v=4zLfCnGVeL4
Its a similar arrangement. S&G solve the problem of pauci-variation mentioned above by picking up the tempo (slightly) with the 2nd verse and switching from an arpeggiated part to a chordal strummed rhythm part. Interesting, considering the suggestions above, this first version of SOS is the basis of the more familiar version as the producer Tom Wilson in June 1965 took the original version of SOS and added electric GTR, bass, and drums - without telling S&G about it. The Byrd's had had a #1 hit the month before with the 1st folk-rock smash Mr Tambourine Man (which Wilson apparently wanted to knock off), and S&G got a big hit as well.
 
Your version has some great vocals. I wish I could do that.
Cheers,
Bert 

Bert Guy
Kevin,
This reminds me of the original version of SOS on the first S&G album Wed Morning @ 3 AM:
https://www.youtube.com/watch?v=4zLfCnGVeL4
Its a similar arrangement. S&G solve the problem of pauci-variation mentioned above by picking up the tempo (slightly) with the 2nd verse and switching from an arpeggiated part to a chordal strummed rhythm part. Interesting, considering the suggestions above, this first version of SOS is the basis of the more familiar version as the producer Tom Wilson in June 1965 took the original version of SOS and added electric GTR, bass, and drums - without telling S&G about it. The Byrd's had had a #1 hit the month before with the 1st folk-rock smash Mr Tambourine Man (which Wilson apparently wanted to knock off), and S&G got a big hit as well.
 
Your version has some great vocals. I wish I could do that.
Cheers,
Bert 

Thanks for the comments.  My own version was inspired more by the original version as that's the version I prefer - in the later version, there's a lot of distortion on the electric instruments which detracts from the beauty of the song, in my opinion.
 
But I am going to see if I can add anything else to the track, using tempo maps etc.  I don't have any hardware synths so I will be relying entirely on Sonar being able to map the tempo accurately, as I didn't use any form of metronome or tempo guide when recording this. 
 
I suppose if nothing else, I could add some extra guitar work and see if that fits at all.