This is a list of optional rebuilds for canon mech designs

Dervish, 55 tons, speed 5
Replace LT LRM-10, Ammo, and Case with ER-LLaser and ECM
replace LT LRM10, 3*Ammo with ER-LLaser, DHS, and MPL,
replace arm SSrm-3 with 3 SLasers, replace FF with TSM
Hitman, 30 tons, speed 7
Replace RT Probe with ECM,
replace LT ECM with C3I,
replace LRM5, Ammo and Artemis with 3 medium laser