Seems like turning it into a 3-banger while keeping the dead cylinder still there wouldn't be really so effective. I'd also be quite concerned about the oil pressure. If you could remove the rod and piston from the dead cylinder and close the hole from the crankcase to the cylinder in a way that wouldn't have any clearance issue with the crankshaft it might work as you may be wanting to. If you do so, should also disable the valves from the dead cylinder.
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