There is also a 64-bit branch of Boxer that is being independently developed.
https://github.com/MaddTheSane/Boxer/tree/updateDosBoxIt is possible that the original developer will come up with a 64-bit release this year, but he has been generally very quiet for the last 3 years.
I have found the unofficial 64-bit build to be stable and fast on my i7 system, despite the claims of performance hits.
Just bear in mind it is based on Boxer 2 Alpha and not the 1.4 release, so any issues or bugs with that have come across as well.
If anyone has trouble compiling, I am happy to share the build I am currently using in macOS 10.14.