[metroschultz]

One of the other guys here is working on that idea also(Diesel John?)
A brazillion years ago, when I was overseas for the Army, I read in one of the Maint. Manuals about a kit the USArmy had for converting a four cyl Jeep (M151) to a two cyl air compressor.
Basically doing what you have described.
Two outer cyl's, #1&4, used for gas engine to drive the unit.
Two inner cyl's, #2&3, used for air pump.
However the Army setup used one way check valves (iirc) for the compressor cyl's.
So the intake and exhaust were split to allow the engine to run off of the two end cyl's.
Then the valve train was modified to keep the valves open during operation (No worry about pistons smacking the valves, these were very loose engines), and check valves put in place to allow air into the two center cyl's through the intake, so it would be filtered, and out the exhaust. then piped to a pressure vessel and used to run all manner of pneumatic tools.
Hope you can make it work.
BTW my 1 litre has very little torque.(it is more than adequate for a tiny car)
your 1 litre should have quite a bit more
bigger pistons X
longer stroke =
more torque
Schultz.