Good, I was going to post about the un-bolted vise, but you have come up with a good work surface. Never use an angle grinder on a piece of un-clamped or hand held steel.When I was a lad, they ran new power lines along the new interstate highway. Cable spools were everywhere. We all had them for work tables, picnic tables, etc. It was not an uncommon sight to see a 10 year old kid rolling one home, down the middle of the street.
My first anvil was a four foot long piece of rail track. Served me well for years. Use six or eight 3"X1/2" galvanized lag screws and washers to bolt it down to the spool (Screw the lag screws in right next to the rail foot, with the washers extending over the foot).Laying down a bed of liquid nails/construction adhesive before you bolt it down will really make it sturdy and may make it quieter.