So basically the Clantech equivalents of most Lostech equipment and construction options? At that point I think you can pretty much just make your own versions of the invasion omnis with the occasional tweak to get around lacking the smaller ER Lasers and having to use Inner Sphere equivalents of non-weapon equipment. (e.g. AMS, Active Probe, ECM, ect)
But since the challenge is for explicitly mixtech mechs I'll start with a mech that is explicitly gaining from both techbases, a Berserker C3 upgrade:
Berserker BRZ-C5
Mass: 100 tons
Tech Base: Mixed
Chassis Config: Biped
Rules Level: Era Specific
Era: Clan Invasion
Tech Rating/Era Availability: X/X-X-X-X
Production Year: 3155
Dry Cost: 33,651,333 C-Bills
Total Cost: 33,651,833 C-Bills
Battle Value: 3,269
Chassis: Unknown Endo-Steel
Power Plant: Unknown 400 Fusion XL Engine
Walking Speed: 43.2 km/h (54.0 km/h)
Maximum Speed: 64.8 km/h (86.4 km/h)
Jump Jets: None
Jump Capacity: 0 meters
Armor: Unknown Standard Armor
Armament:
2 (CL) ER PPCs
4 (CL) Medium Pulse Lasers
1 Hatchet
2 (IS) Small Lasers
1 (IS) Flamer
6 (CL) Machine Guns
1 Angel ECM
1 C3 Boosted Computer (Slave)
Manufacturer: Unknown
Primary Factory: Unknown
Communications System: Unknown
Targeting and Tracking System: Unknown
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Equipment Type Rating Mass
--------------------------------------------------------------------------------
Internal Structure: Endo-Steel 152 points 5.00
Internal Locations: 3 RT, 2 LA, 1 LL, 1 RL
Engine: XL Engine 400 26.50
Walking MP: 4 (5)
Running MP: 6 (8)
Jumping MP: 0
Heat Sinks: (CL) Double Heat Sink 16(32) 6.00
Gyro: Standard 4.00
Cockpit: Standard 3.00
Actuators: L: SH+UA+LA R: SH+UA+LA+H
TSM Locations: 2 RT, 1 LA, 1 RA, 1 LL, 1 RL
Armor: Standard Armor AV - 296 18.50
CASE II Locations: 1 LT 1.00
Internal Armor
Structure Factor
Head 3 9
Center Torso 31 46
Center Torso (rear) 15
L/R Torso 21 31
L/R Torso (rear) 10
L/R Arm 17 34
L/R Leg 21 38
================================================================================
Equipment Location Heat Critical Mass
--------------------------------------------------------------------------------
(IS) Flamer HD 3 1 1.00
(CL) ER PPC CT 15 2 6.00
(IS) Small Laser RT 1 1 0.50
2 (CL) Medium Pulse Lasers RT 8 2 4.00
2 (CL) Machine Guns RT 0 2 0.50
(IS) Small Laser LT 1 1 0.50
2 (CL) Medium Pulse Lasers LT 8 2 4.00
C3 Boosted Computer (Slave) LT 0 2 3.00
2 (CL) Machine Guns LT 0 2 0.50
Hatchet RA - 7 7.00
Angel ECM LA 0 2 2.00
(CL) ER PPC LA 15 2 6.00
2 (CL) Machine Guns LA 0 2 0.50
@MG (1/2) (100) LT - 1 0.50
Free Critical Slots: 1
BattleForce Statistics
MV S (+0) M (+2) L (+4) E (+6) Wt. Ov Armor: 10 Points: 33
4 6 4 2 0 4 3 Structure: 5
Special Abilities: TSM, AECM, C3BSS, MEL, CASEII, SRCH, ES, SEAL, SOA
To activate TSM, run fire the ERPPCs, 2 MPLs and 1 small laser. Then you can run and fire both ERPPCs heat neutrally on the way in. Once you're closer you can switch to walking and firing the 4 MPLs and 1 ERPPC or running and firing 3 MPLs, the flamer and 1 ERPPC. Any time you're short on heat the flamer and the 2 small lasers can be substituted in even if you're out of range to keep things balanced. You're providing C3 spotting to your allies and it takes 2 separate Angel ECMs to shut you down directly. Chase down heavys and assaults and stick the axe in their face for 40 points of concentrated damage that'll armour breach most locations even if you haven't managed to soften them up on the way in and then hose them down with machine guns if they're still standing.
If you had all clantech available you'd probably replace the small lasers and flamer with ER micro lasers and a clan flamer, switch to clan CASE II and possibly swap the Hatchet for Talons, but the difference is fairly modest.