You aren't the only one who has mentioned this, but the others
generally haven't been heard from again.
The first thing you need to do is become able to build 3.4.3 from
source. If you have vintage tools, that should be straightforward,
but if you have more modern ones that don't like various
workarounds the old code uses, it might be tough. However, any
modifications required to get past that are likely to be applicable
to 3.6.x too.
For 3.6, some of the changes to interface code got blindly applied
to unmaintained win/this/ or sys/that/ but went untested. Others
might have overlooked that and will need to reimplemented for
sys/amiga/. The difficulty varies quite a bit depending on the
scope of the changes.
[I've never seen nethack running on an Amiga. Actually, I don't
think I've ever even seen an Amiga.]