From the back cover:
75 tons of devastating firepower. Nothing can stand in a BattleMech's way, except another 'Mech! This book compiles for the first time the BattleTech statistics for the variant Inner Sphere & Clan 'Mech designs. Some are rare, others unique, and each could be that extra surprise you need for victory.
BattleTech Record Sheets Volume 3: Heavy 'Mechs contains heavy 'Mech variants from the 2750, 3025, and 3050 eras of BattleMechs. Included are record sheets for over 45 'Mechs, each with full technical statistics. Included are:
BMB-12D Bombardier
CHP-1N Champion
EXT-4D Exterminator
GLT-5M Guillotine
LGB-0W Longbow
Loki A OmniMech
Mad Cat B OmniMech"
This record sheet pack is one of four that cover all of the 'Mechs detailed in the BattleTech Technical Readout: 2750, BattleTech Technical Readout: 3025 and BattleTech Technical Readout: 3050. It also includes the current Combat Values for the 'Mechs, as at the time of printing.
Although the copyright date states that this publication is copyright 1991, it was actually published in 1990. Despite stating that it includes the Longbow 'Mech record sheet, it actually doesn't the Longbow is an assault class BattleMech, and was actually included in Volume Four of the series alongside the other assault 'Mechs.