Just a few things for you to think about:
1. Turret trucks are "special" application machines especially with a 531" mast = small market potential = low chance to turn over your investment. If the machines were in good shape and there was a good market for them - the dealer who sold the new units would want to keep them to sell as profitable used equipment that consume far more service parts (good profit too) and require service labor (very good profit margins as well) than new equipment. Do yourself a favor ust call a few dealers around town and ask them what the market potetnional is for used "turret" machines w/these specifications, age and hours.
2. It would seem somewhat difficult to transport these machines without some disassembly. You need to know what the overall lowered heights of the machines are. You need to consider not only the dock door heights at the facility they are in so you can get them out, but also bridge/overpass heights limits (if you plan to trnsport on a trailer - standard bed or low boy trailer), and the door heights of facility you plan to store them in. Lifting equipment needed to load & unload? How to load them on a trailer? Or when you say you plan to drive them to a warehouse, hope you didn't mean get on the units and turn the key on and literally drive them down the street.
3. If the units have 14,000 to 17,000 hours on them (which seems quite high to me) and still have 4 to 6 years of good life per the Crown tech why would the customer want to replace them? They are a bit expensive you know.
4. You also need to consider an investment in a charger at the warehouse for these units - meaning charger & electrical hook up expenses, as no doubt the units will need to be charged at a point in time, if you decide to go ahead w/this venture.
5. If you would ask me if I would invest in these machines - I would reply NOT. I advise someone in the used office furniture, liquidated parts and equipment business, over 2 years ago not to invest in two 6000 lb. sit down electric rider lifts w/low hours (less than 3000) but with 276 " 4 stage masts w/batteries & chargers. He still has them - the mast size was a special application mast. The batteries are probably shot now, as he has not charged them.

Just a few things to consider & think about.