The 6-284 is among my favorite cartridges. I do have to offer you some consolation on very short bbl & slow twist.
JBM - Calculations - Stability
^^ here is a link to a stability calculator, this will be your friend
Depending on altitude & velocity, I would imagine the 87grn V-Max would be your best. It should
stabilize (I hope) & offers a decent BC to boot.
I run a 28" 1-8" twist Kreiger with bullets over 100grains only, I can't really help with the load data part.