I converted a 65 Dart to coilovers using a U shaped piece of steel with a hole drilled in the center to bolt it to the upper shock mount. Then drill a hole through cross ways for the shock. Two problems come up with this though. Number one is there may not be enough strength in the upper shock mount area to support the weight and abuse it will take. The other is you are forced to run very short shocks which limited my total travel some.
To help with the strength issue I used a 5/8 bolt for the upper end of the shock. The bolt is very long so I could put some spacers on either side to get out to where I could make some weld on brackets to put that long bolt through, and weld to the frame rail. If you decide to try this make sure you know how much room you will have for those brackets. I put some seriously wide (8.5 x 18) front rims on and it cost me just a little turning radius with only flat plates (1/4 inch) welded to the chassis.