Yes. I did it for the 777.

I'll need more details before I can tell you what you need to know.

Important things to know:

(1)
[Window00]
file_1024=..\..\B737_800\panel\737-800_panel_background.bmp
file_1024_night=..\..\B737_800\panel\737-800_panel_background_night.bmp
size_mm=1024
position=7
visible=1
ident=MAIN_PANEL

gauge00=..\..\B737_800\panel\B737_800!pfd_screen,                    189,548
gauge01=..\..\B737_800\panel\B737_800!pfd,                           210,567,179,179
gauge02=..\..\B737_800\panel\B737_800!mfd_screen,                    409,548
gauge03=..\..\B737_800\panel\B737_800!mfd,                                      430,567,179,179
gauge04=..\..\B737_800\panel\B737_800!eicas_screen,                  740,548
gauge05=..\..\B737_800\panel\B737_800!eicas,                         760,565,179,179
gauge06=..\..\B737_800\panel\B737_800!compass,                          839, 39
gauge07=..\..\B737_800\panel\B737_800!autopilot,                      561,330
gauge08=..\..\B737_800\panel\B737_800!knob_1,                        329,501
gauge09=..\..\B737_800\panel\B737_800!knob_2,                        390,501
gauge10=..\..\B737_800\panel\B737_800!knob_3,                        830,480
gauge11=..\..\B737_800\panel\B737_800!clock,                          77,570
gauge12=..\..\B737_800\panel\B737_800!attitude_backup,                630,444
gauge13=..\..\B737_800\panel\B737_800!adf_vor_backup,                      630,662
gauge14=..\..\B737_800\panel\B737_800!alti_and_asi_backup,                631,555
gauge15=..\..\B737_800\panel\B737_800!gear_lever,                          959,524
gauge16=..\..\B737_800\panel\B737_800!annunciator_below_glideslope,  214,517
gauge17=..\..\B737_800\panel\B737_800!annunciator_le_flaps,          854,516
gauge18=..\..\B737_800\panel\B737_800!annunciator_speed_brake_armed, 516,516
gauge19=..\..\B737_800\panel\B737_800!annunciator_auto_brake_disarm, 823,441
gauge20=..\..\B737_800\panel\B737_800!annunciator_anti_skid_inop,    812,517
gauge21=..\..\B737_800\panel\B737_800!efis_control_panel,                416,344
gauge22=..\..\B737_800\panel\B737_800!flap_indicator,                  892,452
gauge23=..\..\B737_800\panel\B737_800!annunciator_panel_1,                    267,361
gauge24=..\..\B737_800\panel\B737_800!annunciator_panel_gear,            958,454
gauge25=..\..\B737_800\panel\B737_800!Knob_N1_Set,                   755,454

Notice that the images (BMPs) are preceded by ..\..\B737_800\panel\. That is so that it reads the gauges from the default 737. But there is a catch. NOT all the gauges for the 737 are in the B737_800\panel folder, they are in the FSX\Gauges folder so they won't need to be preceded by ..\..\B737_800\panel\:

[Window02]
size_mm=159,441
position=8
visible=0
BACKGROUND_COLOR=16,16,16
ident=RADIO_STACK_PANEL

gauge00=737-400!Comm 1,            0,   0,159, 68
gauge01=737-400!Comm 2,            0,  68,159, 68
gauge02=737-400!Nav 1,                  0, 135,159, 68
gauge03=737-400!Nav 2,                  0, 203,159, 68
gauge04=737-400!Transponder,      0, 271,159, 68
gauge05=737-400!ADF,                  0, 340,159, 68
gauge06=737-400!Audio,                  0, 409,159, 32

Notice that these ones are NOT preceded with ..\..\B737_800\panel\. The 737-400.cab is in the Gauges folder, while the B737_800.cab file IS located in the B737_800\panel. This also applies to the gauges in the [VCockpit0X] sections as well.

(2) So that the VC does not appear jet black, you need to add this line into the texture folder for each variant:

fallback.5=..\..\B737_800\texture

The number (5) MUST be the next consecutive number! So if the one above it is number 3, that line would then become fallback.4=..\..\B737_800\texture.

(3) You need to add this line in the model.cfg in the model folder: interior=..\..\B737_800\model\B737_800_interior

That's the best I can do for now, without more information.

Mark