The biggest thing I'm seeing is you're underestimating your load. Average 50s era full size is 3500lbs, average muscle car is 3000lbs, figure the average 1950-1980 single cab short box pickup is 4000lbs. You toss 3 muscle ats
on a 6000lb trailer and you're at a minimum 15000lbs, possibly as high as 18,000.
Your truck is factory rated at 15,000lbs of fifth wheel or gooseneck, and a Gross Combined Vehicle Weight rating of 23,000lbs.
For reference, on the Cat certified scales, my '05 F-350 CCLB 4x4 weighed just at 7,280 empty stock, with all my gear and me, that number was closer to 7,850. With the family and our 30' 5th wheel I towed from SoCal to North Dakota, all through South Dakota, Wyoming, Montana, Idaho, Utah, Nevada, Washington, and Oregon. We had about 1,000-1,500lbs of room under the GCVWR of 23,500lbs.
Take my 7,850 and add 18,000 from a loaded 48-53' wedge, that's 25,850. Your past single rear wheel trucks ability. By almost a full car.
Maybe go with a lighter 32ft. gooseneck and haul two vehicles and have a margin of safety. You'd just have to find some good deals you could flip for a solid profit when you get back there and it could totally be worth it.
The Current Truck (Oct-2013 to Present):
1999 (Early) F-350 Lariat, CCLB, SRW, Black/Tan
7.3L Powerstroke, 4R100, 4x4, 3.73, 37x13.50-18s, '05 Axle Swap, 6" Fabtech lift, GTP38 "D66" turbo upgrade, SCT 4-position chip with custom tuning by me, Straight Piped 4" down pipe through 5" dual stacks, N-Fab full length triple steps, Pro-Tech cab guard and tool box, louvered 5th wheel gate, Hella 500 Fog and Driving lamps, much more to come...
The one I'll miss, (Mar-2009 to Jan-2014):
2000 Excursion XLT 4x4
6.8L V-10, 4R100, 4.30, 285/75-18, 271whp / 388wtq
The one I won't, (Jul-2005 to Sep-2012):
2005 F-350 XLT, CCLB, SRW, 4x4 FX4
6.0L PSD, ZF-6S650, 3.73, 35x12.5-18, 4.5" Lift