Wait.. so you want to put a bumper-pull coupler onto the front of a fifth wheel type trailer..? That seems like a "Bad Idea!"
Any chance you could borrow a dolly aka converter gear? Those will often have a lunette ring for pulling, and they're designed to carry most of the pin weight of the 5er so that the pintle on the towing vehicle is carrying little of the trailer's weight. If not borrow, then maybe create one by rigging a fifth wheel onto the deck of a conventional bumper-pull trailer..?
How long a reefer are you talking? 27 ft? 53 ft? Here
is a table of various trailers. They list a typical 53 ft reefer as 15,500 pounds tare. I'm not very good at visually estimating weight distribution, but this
place recommends pin weight should be 18%-20% of the trailer weight. Supposing that holds for the big 5ers too, and that it's balanced that way even empty (don't forget there's a heavy reefer bolted onto the front wall), then maybe it's in the neighborhood of 3000 pounds pin weight?
The rear axle(s) on the reefer might be adjustable, and sliding them as far forward as possible will reduce the tongue weight. Supposing a hitch arrangement can be crafted to carry that load.. a pintle and lunette maybe; I'm not sure a ball type coupler would survive carrying so much tongue weight.. it will also unload the front axle possibly to the point that steering doesn't work reliably.