For a true 1/2A fuselage you can use 1/16" balsa sides.  For something quite large in the 1cc range you might go up to 3/32". The basswood is likely to be 2.5 times the density of balsa, best case. To try to keep the weight under control you would need the basswood to be 1/32" or thinner. My estimate used 8 lb balsa and 20 lb basswood. Go measure some pieces if you get serious about this.

The problem that you get into applies not only to models, but to full-scale aircraft design--what mass props guys call "minimum gauge."  To get to an equivalent weight in a more-dense material you end up so thin that you have problems with buckling, problems with manufacturing (assembling), even making the parts. That can be dealt with in some ways with chemical milling of aluminum sheets, but....  In the basswood vs. balsa tradeoff I think you are looking at a serious challenge to avoid a lot of weight growth. Instead, I use 1/64 ply doublers inside the nose area and balsa sides. One of the main purposes is to spread out the loads from the engine mounts. To be effective, you need better tearout strength than just the balsa--the spruce or maple engine mounts glue very nicely to the birch plywood. If you keep the weight of the glue down, it works fine and is quite durable. Let me look and see if I can find a picture of that.

Just my thoughts, good luck with your project!

Dave