DOn.. forget about centering the car over the trailer axles..
thats BS... with the trailer and truck LEVEL.. then put the
car on the trailer...take it to get the total trailer/car weight
and based on that number move the car fore and aft to get 10%
to 15% MAX on the tongue... you might need lift bars.. when you
put the bars on you bring the back of the truck and the front of
the trailer back up to LEVEL.... in MOST cases you will find that
the top of the ball will be at 19" to keep the trailer level.. once
you find that load balance point.. mount a set of stops for the front
wheels... I wont tell you I know what I'm saying.. but years ago I did
trailer design for U-Haul

A 16' open beavertail has been my Duster's trailer for decades. Overhangs the rear a bit with the weight basically as Mr P says. Ft tires about 6" or so aft of the ft edge of the deck, where I bolted some wheel chocks.
I've had my Road Runner & my '63 & '64 Savoy wagons on it, but found the limit with a long-bed '68 Chevy pickup...rear wheels were close to the rear edge of the deck, barely fit.
I mounted a PU-truck toolbox forward of the ramps, a floor-jack tray between the box & the ramps, and an electric winch inside the box (hole in rear wall for cable).
Tows fine, and the box is also handy for some of the race stuff, tie-downs, etc.
An antenna & antenna-ball I mounted near the coupler makes it easy to line up for backing the truck up to it. Reference decal centered in back window of the canopy/bedcap.

I think a Duster/Demon has a 110 in. wheel base. My D50 also has a 110 in. wheel base and when I put it on the trailer so my tow vehicle (Dakota) is level the front wheels are a little more than 5 ft. from the head rail. I just measured my trailer and it is 15 ft. flat with a 3 ft. dove tail. My back tires are just barely on the flat part of the trailer. Best towing trailer I have ever owned.

A Duster has 108" wheelbase. Our Challenger has 110" and it also fits on a 16' trailer.

My B body on a 16'

Back

I have to figure out a shorter strap deal for the front. The eyelets are cose to the tie down point.

NO. The Duster was 108" (9'), the shortest A body was 106" (8'10").

I had a 13'10" trailer that I hauled A and B bodies with.
When I built it, I mounted the axles so I could load a B body all the way to the front of the runners and a A body about 6" further back. The back of the car hung past the end of the runners a bit, this bothers some, I don't know why it matters as it doesn't effect towing.

I now have a trailer with 16' runners and a tool box (2'deep-2.5'long-5'wide) in front. I wish I had my old trailer back, it weighted less, pulled better and took less room to store.

A-bodies on a 16 foot trailer are no problem at all.

I've carried stuff a lot larger on my 16 foot trailer.



It handled fine, speed of about 60-65.