I have an older home, built in 1930. I would like to replace the old toilets with low flow toilets. My problem is that the old toilets sit out from the wall, about 16" to the drain. The tank is separated from the bowl by a 4" pipe. Other than building out the wall behind the tank, is there any other remedy for this situation?

You can purchase low flow toilets that have the same look as the older ones. With the metal pipe that connects the bowl to the tank.
Otherwise you will need to cut open the floor and install a new pipe from the wall out to new drain opening location.
They do sell offset flanges that can be inserted into the old pipe, however this will only give you about two inches.