putting a 68 convertible back together and I'm having problems finding the correct spacing between quarters, doors, fenders, etc. Is there a diagram somewhere or what is the procedure?? thanks.

The correct gap specs are listed in the factory assembly manual, 3/16" to 1/4" is pretty much accepted as good.

If you look in the basics sticky at the top of body, there is an excellent series by Brian Martin, one of which covers panel alignment very well.