<< To my knowledge, only regular Athlons (Shown as "Slot-A") will work in that motherboard. The Thunderbird core is regarding the Socket 462 Athlons. >>
There are SlotA Thunderbirds as well, though not a large number were made.
The K7M-RM will work with a SlotA T-Bird, though I'd be a little wary with a T-Bird beyond 800MHz in one. In my experience most SlotA boards had some issues with T-Birds past 800MHz.