Nothing would be easier than running a .284 mandrel through a 6.5rpm case. Get bushing dies for 6.5rpm and put an appropriate 7mm bushing in it. People have already done that and there's a reamer.... like this one.
7mm x 6.5 WBY RPM Sretched out 284 Winchester case made by Weatherby. Chamber Reamer rental
4drentals.com
Looking around online it comes in at 78.9gr case capacity. About 5gr more than 280ai, 3ish less than 7rm. So In between those, closer to 7RM. If you ran it in a chassis with the mdt magazine, you can seat those bullets a bit longer.