[Diesel_Dave]

I believe that mechman600 is correct (at least for an inline 4). Generally 1 & 4 are positionally the same (but on different strokes--360 deg apart) as are 2 & 3 (180 deg off from 1 & 4. This is similar to an inline 6 where 1 & 6, 2 & 5, 3 &4 are together. I know an inline 6 can be run on either 1-3 or 4-6. Generally there's some additional vibration, but I believe it's tolerable.

So I believe it would technically be possible. That being said, it's going to be a ton of work, for not a huge amount of gain. To do it right, you should deactivate the valves and drill holes through the deactivated piston. And after you're done, you'll still have frictional losses pretty much the same as before, and the thing will probably take forever to warm up. Plus you'll still have all the weight of the original engine.