Giaffess;
knowing now that you want to convert a power boat trailer into a sailboat trailer, I now have posted your photo which you sent to me. First I do not like advising how to do this as most people do not know how to weld nor have the expertise to refit a trailer like this as there are many variables. To simply attach jack stands temporarily I can tell you no. Without a keel tray the answer is no. I assume you are talking about an Oday 272LE which I think is a fixed keel or a 23 Oday with fixed keel. Is so, then I will make suggestions but under no conition I will except any responsibility. So I will speak in general terms.
The idea of moving your boat on a flatbed with cradle is excellent but we do not know the conditions or where the boat will be moved. Then of course will it be under 13 feet and 6 inches with no mast up. If mast up, is there any overhead obstruction like trees, overhangs, wires and so on.
You trailer would have to be modiefied with a keel tray to carry the weight of the boat. Any type of stands will need to be permanently affixed to the trailer to support the hull up. Then of course the positioning of the stands is important so they will not flex the hull inward. Three needed each side if long distance traveling. I suggest three each side regardless if using adjustable stands or adjustable bunk boards. Then you need to configure where the boat will sit so there is 10% of the weight on the tongue (total weight ) so the trailer will not swerve even though this is a dual axle trailer. Then of course if you do not know how to weld is another issue. A lot of questions my friend. I will invite others to give imput but at least this is a start. One other if trying to launch or retrieve without an extension, the boat will need to be hauled. Like I said, any stands will need to be secured permanently. One other thing. If you weld a keel tray to the undercarage or cross supports, you have to make sure with the weight of the boat on the trailer, nothing interfers with the dual axles.
Not sure if this is the correct trailer as this is a painted trailer vs. galvanized
Crazy Dave Condon