I don't remember every buying any Allison parts that didn't have the same part number with both Allison and GM.
In almost all cities there's a 3rd party Allison dealer that isn't the GM dealer so they cannot carry Allison parts, they always bring out their acdelco equivalent at 4x the price. both internal and spin on filters have separate Allison and acdelco part numbers and vastly different prices.
Now if the number turns out to be the same, you'll get an Allison brand from an Allison dealer but an acdelco brand from a GM dealer, the acdelco might be a reboxed Allison but there is no way of knowing. I trust acdelco but when it comes to my trans I only go with Allison filters
My suggestion, go straight to an authorized Allison dealer and ask for the filter, chances are it will be close to the same price as the interwebs Allison is good about not letting their dealers jack up prices.