Several Nikon lenses including the 180–400 have the same two size screw fitting.
Try searching Amazon for a Mantona AS – 100 - 2M.
It has two screws, one for each thread size, and a modest amount of travel to help balance on a Gimbal.
There are other options which appear to have the 3/8 screw permanently fixed at one end, making it challenging to balance the rig on a gimbal or tripod head.
The long plate that comes with a Gitzo GHFG1 gimbal is both better and worse.
At 5.5 inches long it has plenty of travel.
The machining of the two screws would probably be unacceptable to the cheapest Chinese knockoff shop and the 3/8 screw fitting is by inserting a half inch screw and then screwing andouter 3/8 adaptor in place – hardly the best security for an expensive lens.
The rubbers on the QR plate that provide friction between the plate and the tripod mount can easily be lifted with a fingernail.
The Gitzo literature with Gitzo products proclaims the companies aim is to "design and produce the best possible camera accessories and supports using the simplest, most straightforward and most elegant solutions --- however long and complex the path to get there".
Whoever designed this plate was not listening
The friction adjustments on the Gitzo gimbal are not much better - at just about adequate.
My other Gitzo products are excellent quality - as as one should expect at the price point.
