I have seen a wheel lift added to a obs chevy wrecker but not one that has been put on a obs ford. What I do know from that is you will want the pivot for the lift as far foword as you can, preferably in front of the rear axle. If this pivot is to far back you will lift the front wheels off the ground and will make the truck unsafe to use. With the photo you gave, that cross meber above the axle needs removed and you might get away with having your pivot a ~1ft forword of that. You will also want to add waight to your front bumper as well to aid in keeping the noise down.
EDIT: This is is a quick photo I found, may be a different truck but is good example of mounting the lift with the pivot in a ideal point.
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