Manuel, Yes, its very tight. When I remove the nut on the central shaft, I remove the tool head, but then I put the crankshaft assembly back on, secured with the taper pin. They with suitable padding (like strips of heavy leather, I clamp head of the crank shaft assembly in a vice to keep the shaft from rotating while you loosen the nut. In some cases, I have applied some heat to the nut with a propane torch, but usually it isn't necessary.
If there is a bushing, you should be able to hook it with a bent paper clip and pull it out from above. Only if its held in place by oxidized grease is it necessary to remove the aluminum base to get at it. If the hole has straight walls, there is no bushing. If the walls of the hole are tapered inward, then a bushing is installed.