One reason he uses openssl is to help teach that in process substitution, the contents of <( ) can be pipeline. If you relax his didactic requirement, join's options let you do the job with a lot less typing.
$ join -j2 -o 1.1,0,2.1 <(sha1sum *) <(wc -c *)
Note that sha1sum has the same output format as wc -c, which makes the join easier.
Non-Linux boxes might not have sha1sum, but if I didn't have it, I'd see if I had md5sum, which has the same output format. Their Wikipedia entries say these commands are widely available on lots of non-Linux OSs.