I have created an improved retrofit panel over my last "version" for Captain Sim's 727-100. This retrofit will work with the -200 and Freighters, but you will have to customize the panel.cfg for those models.

I managed to integrate the freeware TCAS II gauge from flightsim.com (search: TCAS II gauge), an ISG EHSI and the EHSI Controller, FMC, MCU and I also have FSXPaul's V-One gauge installed (Awesome work there Paul!)

Remember to back up your 727 panel.cfg before changing anything.

Follow the steps in the TCAS II folder for installation. Thanks too Lee Hetherington for his awesome TCAS gauge!

Make sure you have the heading select on before you activate the LNAV. ISG's LNAV system will give commands to the aircrafts heading select automatically.

Aircraft.cfg mod, so the ISG screens don't turn off in flight.

[electrical]
electric_always_available=1 //add this under electrical section

The new panel.cfg for the 727-100

Replace XX with next value.

New window titles:

[Window Titles]
WindowXX=EHSI CNTL
WindowXX=ISG1 MCU
WindowXX=ISG1 FMS

Radio panel with new Transponder selector:

[WindowXX]
size_mm=349,845
position=8
background_color=25,0,0
visible=0
windowsize_ratio=0.75
ident=RADIO_STACK_PANEL
gauge00=Captain_Sim.p721.P10!P10_001_vhf,  0,  0,349,190
gauge01=Captain_Sim.p721.P11!P11_001_vhf,  0,190,349,190
gauge02=ILH_TCAS!Transponder, 0,380,349,155 pic:no
gauge03=Captain_Sim.p721.P01!P01_001_adf,  0,535,349,155
gauge04=Captain_Sim.p721.P07!P07_001_adf,  0,690,349,155

ISG FMC, MCU, and EHSI controller:

[WindowXX]
Background_color=0,0,0
size_mm=300,100
position=0
visible=1
ident=4007
gauge00=ISG1!EFS50_EHSI_CNTR_LM, 0,0,300,100

[WindowXX]
Background_color=0,0,0
size_mm=312,214
position=4
window_pos= 0.1541,0.3133
window_size=0.1888,0.2044
visible=0
ident=4001

gauge00=isg1!MCU,  0,0,312,214

[WindowXX]
Background_color=0,0,0
size_mm=140,271
window_size_ratio=1.000  
visible=0
ident=4004
window_pos = 0.7402, 0.4122
window_size= 0.250, 0.500

gauge00=isg1!SMITHS_FMS,  0,0,140,271

VCockpit modifications:

[VCockpit01]

gauge07=ILH_TCAS!IVSIb, 16,520, 219, 222 other:45 pic:no
//gauge07=Captain_Sim.p721.L11!L11_vsi, 20,524, 217,220

gauge14=ISG1!EFS50_EHSI_NB, 609, 414, 183, 176
//gauge14=Captain_Sim.p721.L08!L08_hsi, 599, 399, 199, 239

gauge27=Captain_Sim.p721.R15!R15_001_dme,      499,799, 90,30 //DME switching as mentioned by CoolP

gaugeXX=ILH_TCAS!Logic, 0, 0, 1, 1, volume:-200 //add at the end of VCockpit01 section

[VCockpit07]

gauge05=ILH_TCAS!IVSI2b, 12, 516, 219, 222 other:45 pic:no
//gauge05=Captain_Sim.p721.R11!R11_vsi, 20,524, 217,220

gauge22=Captain_Sim.p721.L15!L15_001_dme,      499,799, 90,30

It helped a lot on vatsim with reducing some of the "virtual pilot's" work load. Of course, you can add it to any aircraft in FSX.   The TCAS gauge is freeware from flightsim.com - I highly recommend it, it works well with vPilot, too.