It all depends on which direction the door has to move (in 3 dimensions). You really have to sit there and see where it's out to begin with, then determine where to put the shims and how thick they should be.
I aligned the doors on the red Speedster that Alan finished and all I used was some flat aluminum stock 2-1/2" square or so. Sometimes it goes between the door and the hinge, sometimes between the body and the hinge, depending on which door corner you're trying to move and in which direction.
A very little difference in shim thickness and where positioned can make a BIG difference in the end result, so go slowly and play with different thicknesses until you get it to where it looks cool.
Thanks, Gordon! Your info makes sense. I'll put this on 'the list' of tasks to tackle. Now that the seal has arrived I'll turn my attention back to getting the ole girl up and running again.
Jan - I know it seems like I'm all over the place on this car. I like to keep myself busy while I'm waiting for parts.
I started to tear into the oil system as part of an overall project to keep the motor cool and attack a few small oil drips. With the proper Gene Berg oil pump cover, the new 'step stud' on the sump and the 'red seal nuts' on the oil pump - I hope to have solved my oil drips. I uncovered the sand seal when I was trying to install the proper 7" crank pulley. Previously I had no idea the motor was running a sand seal. Once I discovered the seal was leaking I decided to replace the seal and put a proper sized sand seal pulley on the car.
Naturally, while the oil was out, I figured it's the right time to install the cooler and thermostat. With the stock sized pulley, the cooler, the thermostat, the fan, etc. - I should be able to help keep the temps down into comfortable levels. Granted, it was't bad before - I just didn't like watching the temps go up while sitting in traffic.
I've also been planning on sealing up the rear most area of the engine compartment. It's always bothered me that it was 'open' the the heat from the header. A 38" x 4" gap can let in a lot of heat while sitting in traffic. Gotta keep the hot side hot and the cold side cold. 
I decided to tackle the dingy back end because it's the first thing I see as I pull and out of the garage every single day. Also the wires are in the visible as I'm dealing with both the waxing of the rear of the car AND sealing up the rear of the body/engine tin.
Ted