AFAIK there is a major problem with that solution. All the major manufacturers design their units using a joint/proprietary methodology and not split/modular.
What that means is that you have a good 90% chance that all the critical subsystems (stepper motor mechanism control circuits, display control circuits, etc.) are all fused together in one and only control PCB. It will be extremelly difficult to seperate or control those circuits individualy.
Best case scenario is that you get a fully working unit and just exchange the LCD module/vga controller. Other problems arise with that:
1) Most of the motorised factory units are 6.5" not 7"
2) Is it cost effective ? (you'll need a fully working unit to hack)
3) There is no way for you to be sure if the control board wants to "see" the specific LCD module and if they communicate (unless you can get your hands on a service manual)
4) Will it be enough room there for an extra PCB (vga controller) and possibly a tsk controller ?
I don't want to discourage you but I believe there are some things you should think of before doing something like that.