I think I like the banded mail option and +3 NA.
40 ft speed is fine.
How about Str 18, Con 15, Dex 10, Int 12, Wis 13, Cha 13?
Hmm… I'd be fine giving it a slightly better AC than 20 since translating older edition monsters to 3E often gives them higher numbers than the original.
So I could see us going
+2 banded mail, +4 natural and Dex +1 for AC 22.
As for the ability scores, I'm wondering about making Wisdom hgiher than Charisma. A Minotaur has Wisdom as its highest mental stat (Int 7, Wis 10, Cha 8) and its Intelligence is its lowest number.
These are supposed to be minotaur-like, aren't they, so perhaps their mental ability scores have the same relative values, just five points higher for Int 12, Wis 15, Cha 13?
Those numbers are pretty close to a low-rank Demon such as a
Babau, which is what these things are supposed to be, although the Constitution might be a tad low. A Babau Demon has Str 21, Dex 12, Con 20, Int 14, Wis 13, Cha 16.
Maybe make the Con higher? Like 19?
Putting that all together would make Str 18, Dex 12, Con 19, Int 12, Wis 15, Cha 13.