Having played it (great job!), this actually could be optimized all the way down to an 8088, as the playfield doesn't scroll. A challenge for the next CGA JAM, perhaps. :)
This certainly could be worked to run on a 8088, but I only have a 486 at my disposal. Also, I'm still not sure if modern versions of DJGPP are still capable of generating real mode code (used GCC 7, cross compiling from Ubuntu).
Anyway, I'm certainly not done with DOS Game Development :)
You have a few options in 2017 for making 16-bit DOS games coming from a 32/64-bit GCC background: An old 16-bit compiler like Borland C or Turbo C; OpenWatcom which can compile to a 16-bit output; or probably the best option, a newly-released toolchain based on GCC 6.2 available here: https://blogs.mentor.com/embed... (if the link didn't make it through, google for "Sourcery CodeBench Lite for IA16").
My DOS retrocoding is in a mix of Turbo Pascal and assembler, as the TP IDE allows coding/debugging on the old hardware itself. But I'm old, and quite insane.