SpaceCat, while you're not wrong, you'd be the only heavy with an XL. For that XL you are only gaining a little bit over not having it, not making it really worth it.
If i was doing XL, i'd do this
Orion ON1-LTC
Mass: 75 tons
Tech Base: Inner Sphere
Chassis Config: Biped
Rules Level: Experimental Tech
Era: All Eras (non-canon)
Tech Rating/Era Availability: E/X-F-E-D
Production Year: 0
Dry Cost: 15,918,438 C-Bills
Total Cost: 16,018,938 C-Bills
Battle Value: 1,707
Chassis: Unknown Endo-Steel
Power Plant: Unknown 300 Fusion XL Engine
Walking Speed: 43.2 km/h
Maximum Speed: 64.8 km/h
Jump Jets: None
Jump Capacity: 120 meters
Armor: Unknown Standard Armor w/ CASE
Armament:
1 Long Tom Art. Cannon
1 Large Pulse Laser
1 SRM-6
1 Medium Pulse Laser
Manufacturer: Unknown
Primary Factory: Unknown
Communications System: Unknown
Targeting and Tracking System: Unknown
================================================================================
Equipment Type Rating Mass
--------------------------------------------------------------------------------
Internal Structure: Endo-Steel 114 points 4.00
Internal Locations: 1 HD, 2 CT, 1 LT, 6 LA, 4 RA
Engine: XL Fusion Engine 300 9.50
Walking MP: 4
Running MP: 6
Jumping MP: 4 Standard
Jump Jet Locations: 2 LL, 2 RL 4.00
Heat Sinks: Double Heat Sink 10(20) 0.00
Gyro: Standard 3.00
Cockpit: Standard 3.00
Actuators: L: SH+UA+LA R: SH+UA
Armor: Standard Armor AV - 224 14.00
CASE Locations: 1 LT 0.50
Internal Armor
Structure Factor
Head 3 9
Center Torso 23 36
Center Torso (rear) 9
L/R Torso 16 24
L/R Torso (rear) 8
L/R Arm 12 24
L/R Leg 16 29
================================================================================
Equipment Location Heat Critical Mass
--------------------------------------------------------------------------------
Long Tom Art. Cannon RT/RA 20 9/6 20.00
SRM-6 LT 4 2 3.00
Medium Pulse Laser LA 4 1 2.00
Large Pulse Laser LA 10 2 7.00
@Long Tom Cannon (15) LT - 3 3.00
@SRM-6 (15) LT - 1 1.00
@SRM-6 (Inferno) (15) LT - 1 1.00
Free Critical Slots: 0
BattleForce Statistics
MV S (+0) M (+2) L (+4) E (+6) Wt. Ov Armor: 7 Points: 17
4j 2 3 2 0 3 2 Structure: 3
Special Abilities: ARTLTC, CASE, SRCH, ES, SEAL, SOA