Funny, I was fiddling w/ the same thing, here is what I came up w/ for the flight_model.cfg file (located here for normal STEAM location; \Microsoft Flight Simulator\Packages\Community\workingtitle-aircraft-cj4\SimObjects\Airplanes\Asobo_CJ4)
empty_weight_pitch_MOI = 46001 ; 69403 Empty pitch moment of inertia, Jxx (SLUG SQ FEET)
empty_weight_roll_MOI = 43001 ; 13434 Empty roll moment of inertia, Jzz (SLUG SQ FEET)
empty_weight_yaw_MOI = 18601 ; 75997 Empty yaw moment of inertia, Jyy (SLUG SQ FEET)
empty_weight_coupled_MOI = 0 ; 100 Empty transverse moment of inertia, Jyz (SLUG SQ FEET)
I have no clue if these are actually used in the FS flt model, but I changed them to match the empty weight POH values
[REFERENCE SPEEDS]
full_flaps_stall_speed = 71 ; 90 Knots True (KTAS)
flaps_up_stall_speed = 81 ; 105 Knots True (KTAS)