First, visit a scale and weigh the 3500 in the configuration you will be towing it. Then, see what the towing capacity of the vehicle you plan to use to tow it is. If that matches, then find a towbar of the necessary capacity. Based on the known weight of my 2500 (about 7900 lbs.), you will quite likely need a towbar with 10,000 pound capacity. Before you buy the towbar, shop around for a driveshaft disconnect for your truck. If such a disconnect is not available, it is possible to get under there, remove the driveshaft from the differential yoke, wrap the U-joint with tape to hold the bearing caps in place, and tie the shaft firmly out of the way. I did that years ago, when towing a Datsun pickup. It took about five minutes to remove the shaft before towing and replacing the shaft when ready to drive the truck.