I just got replied in the Mental Omega Discord channel by @Morton :
in art/artmd/artmo INI there are "sequences" that contain what you want
i.e.
[GISequence]
Ready=0,1,1
Guard=0,1,1
Prone=86,1,6
Walk=8,6,6
FireUp=164,6,6
Down=260,2,2
Crawl=86,6,6
Up=276,2,2
FireProne=212,6,6
Idle1=56,15,0,S
Idle2=71,15,0,E
Die1=134,15,0
Die2=149,15,0
Die3=0,1,1
Die4=0,1,1
Die5=0,1,1
Deploy=300,15,0
Deployed=292,1,1
DeployedFire=315,6,6
DeployedIdle=0,0,0
Undeploy=276,2,2
Paradrop=363,1,0
Cheer=364,8,0,E
Panic=8,6,6
starting frame,length,offset to the next facing
so for Walk=8,6,6 it's "start at frame 8, use 6 frames per facing"
there are 8 facings, starting from north and going counter clockwise
if an animation doesn't have facings, it will have 0 as the third value, i.e. Die or Deploy
Idle1, Idle2, Cheer have a special case where the 4th extra value is S (south) or E (east), but I don't know if that's used at all