I believe I have come up with a livable alternative for me. A new spell, usable Clerics and MU's called "Know Thy Enemy". When a Cleric or MU casts the spell (presumably the first thing they do) they are able to know who or what it is and the AC of the opponent is made known to the spellcaster who can then inform the rest of the party if they so choose to do so. Knowledge is power after all.
At that point, a Player can then make use of THAC0 information to know for themselves what they need "to hit" and maybe even get a +1 bonus for the knowledge (I haven't made up my mind on that last bit yet).
To gain that information costs a spell caster a spell slot for the day though and I am likely to make it a
The item in question will be an "eye" tooth/fang from a defeated opponent. The tooth will crumble into dust upon casting the spell. The tooth will have to be obtained by the spell caster themself in order for it to work.