Best location for 4 speakers

[lsversaw]

I've read most of the posts here about speaker locations...kick panels, doors, original center-dash (mono or stereo), rear cab corners, front "fill", underseat. I haven't seen an answer to this specific question, though...

If you have four speaker outputs -- and only four -- from your head unit or amp, where's the best location, size, and shape for the four speakers?

My assumptions -- reasonable minds may differ -- are:
- Semi-original looks are preferred; any modifications should be low key, maybe not even noticable.
- I'm not interested in the SPL wars (if you are, fine, but please be respectful of others).
- I'm not interested in boosting bass. I don't select music based on bass content.
- I'd like reasonable sound quality, and a sense of being surrounded by sound. But I don't believe in trying to reproduce the original sound stage or imaging within the confines of our truck cabs. I'm looking more for a surround-sound experience than a concert-hall experience.
- I've got a '72 C20. Love it. A real truck.
- I'll eventually install some vibration damping and sound reduction stuff.
- Cost is always a factor, so I'll say a limit of about $1000 for the speakers themselves AND kick panels, if purchased. Not counting sound reduction material. Also not counting installation labor; I'll do that myself. But I'm not willing to pay more than $500 unless the additional cost results in "better" sound. To me, better means wider frequency response, flatter frequency response, and a sense of sound coming from everywhere, not just the speaker locations.
- I'll move my gas tank, so rear corner speakers are an option.
- I consider a set of 2- or 3-way component speakers with a passive crossover as one speaker.

If there are other assumptions required to give an answer, let me know.

Let's have fun with this!