The kits from mustang places make a great list of things that can be done and parts needed. I would take the list to an autoparts store or shop on line with a general parts store. I'll bet you can piece together a system that's better quality and more economical than the kits.
- Agree that poly bushings for the strut bars are a NO-NO. Or you can replace the bars with adjustible units ala
http://home.bresnan.net/~dazed/adjustable
- Check out Tinman for the subframe connectors.
- Monte Carlo bar is high on the up grade list. I lile the combination one but not enough to change out the export brace/MC bar I currently have.
- In the research I've done recently, performance
suspension builders seem to be favoring lower stiffness springs and stiff shocks. Do some reading on this, a lot of information is available on the net. The PO of my car installed Gabriel shocks and Pro Motor sport progressive rate coils. Rides good and I've pushed the car through corners pretty good and haven't found the limit. (I'm saving that experience for sometime when I'm not on a public road.)
https://www.pro-motorsports.com/store/front-coil-springs.asp
- I've heard a lot of good things about the Opentracker roller spring perches, and would definitely give those a look.
http://www.opentrackerracingproducts.com/
- Along those lines also consider the "improved" idler arm.
http://www.stanginfo.com/Reviews/Moog/Moog.htm He says pitman arm in the article but clearly he is refering to the idler arm. The write up is for a 67, the NPD catalog shows the same stock replacement part for the 67 and 68 idler arm, so it should work.
- A larger front sway bar is generally considered a good thing. However, a rear sway bar increases traction of the rear tires, which is a good thing unless it promotes oversteer, which can bring the rear end around faster than the driver can react. Use the rear sway bar as a tuning device. Set up the rest of the components first and if you have issues with too much under steer, then consider a rear bar. Note the stiffness of sway bars increases to the 4th power of the diameter of the bar. Going from a 1" bar to a 1 1/8" bar doesn't sound like much but the latter bar is 60% stiffer! (Assuming the rest of the geometry is the same.)
- Shelby mod already mentioned - good and free. Be sure to use the right diagram for a 68, it's different than for the 65-66.
Of course not much matters unless you have good tires and a proper alignment. If you do some of the mods suggested here you may not want to use "stock" alignment specifications. Post the mods and let the experts give you alignment recommendations. Good luck on finding a shop that cares enough to do the alignment right!
PC I'm not a professional mechanic or mechanical engineer. Do your own research. All of the above are suggested items to examine - not recommendations.
Poly busings in general doesn't appeal to me either.
Look into a monte carlo bar for added stiffness up front 
