This is the armorers wrench I used. Did my best to keep it square but at when you are nearly standing on it that is a challenge.
Also pictured is a Magpul Industries BEV Block Accessory that has barrel extension support.
I need a new vise block for this exact reason. Do you recommend the Magpul one? I broke my last upper block and haven’t replaced it yet. Still have an AR torn apart needing to get put back together.