Alright, in case it interests anyone else, I've figured out the Battlemechs from the first set, mostly thanks to the pilot dossiers which give some actual specs:
Arbalest = Just a regular Arbalest.
Atlas = AS7-K2, but listed with heavy instead of ferro-fibrous armor.
Black Hawk = D configuration.
Catapult = CPLT-C2.
Centurion = CN9-Ar. Could maybe be the AL, but it's probably meant to be the Jihad mech. Somehow has endo steel and ferro-fibrous armor.
Cougar - Probably the B configuration, but it's missing the ER medium laser.
Firestarter - FS9-M2. Santiago Padilla's entry gives it a loadout I don't think exists (2 flamers, an LB-X 10, and a "light laser"), but the entry mentions it having 6 flamers later so I think the odd loadout was a mistake.
Hatchetman - HCT-5D
Jupiter - Jupiter.
Koshi - Koshi.
Legionnaire - LGN-2D.
Mad Cat III - Version 4.
Pack Hunter - 2.
Panther - PNT-10K2.
Ryoken II - Ryoken II.
Spider - SDR-8K.
Tundra Wolf - Tundra Wolf.
Zeus X - ZEU-X.
Doing this has really made me kind of hate the number of variants old mechs have. Trying to find the right Atlas and Spider hurt me in ways you wouldn't believe.
I'm trying to work through the Industrialmechs next, but some of those are even worse to figure out (looking at you Miningmech and Miningmech MOD).
EDIT: Several corrections.
EDIT 2: Apparently, while across the unique pilots all mechs of the same model seem to be the same variant, the same can't be said for across factions. Case in point, the Dragon's Fury Centurion is probably the -D3D, not the -Ar. Ugh.