The article I had read a while ago described fixing the intake valves shut, and removing the exhaust valves. Shutting all valves will result in a parasitic cycle of pressure/vacuum on the deactivated cylinders. This allows the deactivated cylinders' pistons to just "bounce" up and down on air.
If you take the exhaust valves out, you'd also need to plug up the exhaust valve guides to keep from pressurizing the crankcase with exhaust coming from the active cylinders.
Read about this in the 60s-Mother Earth News. Only disabled intake valves on 2 cyl. Exhaust valves opened/closed normal. Was easy to do but no data on performance. They at that time supported complete conversion to methanol/menthanol? and operated cars, trucks, generators and even flew a small plane to D.C. to promote this renewable resource. Should have listened then. Maybe the arabs wouldn't own us now?
You have to do 4, or you will be putting an unbalanced load on the crankshaft. The engine will not run smoothly. Some modern engines do this, but I believe the computer varies which cylinder is deactivated each revolution.
Yeah, there's plenty of modern and old examples of Displacement On Demand technology. GM's current V8 engines equipped with AFM (Active Fuel Management) will go to 6 or 4 cylinders as necessary.
If you let the exhaust valves operate normally, you will waste energy pulling the pistons against a vacuum and suck in exhaust which will mess up exhaust flow. You have to close all the valves (thereby making the piston into an air spring that releases almost as much energy as it stores).