I built my first model aeroplane, a Keil Kraft Ajax, about 57 years ago. Since then I've built thirty or more models from kits, plans and plan-packs as well as rescuing lame dogs and other people's unfinished projects. However, the Baron 1914 is the first model I've ever built where only one wing-half is shown on the plan. Nowadays you can take the plan to Office World and have a mirror image printed but traditionally we smeared the underside of the plan with paraffin, kerosene in American palance, and hey presto, you've got the other wing-half.
That's exactly what I did this afternoon using white spirit. It smells a bit but does the job. Pictures show the port wing under construction. The slots in the wing ribs are an extremely tight fit on the spars. To speed things up I have used cyano glue to build the wing which is a first for me.