Hi Dr. Panga

Taking an existing, 6040,3040 machine apart to build a bigger machine, I think would be no good.
About the only thing you would not need to modify is the control electronics & motors.
The control electronics of those ebay chinese 6040/3040 routers are notoriousy cheap and nasty. Most people replace them immediately!
Most of the rails,ballscrews,gantry would need to be replaced. You might be able to use some of the bed, but 80%+ of the machine would not be re-used.

I would look at either buying a machine at the right size for your needs, or building your own from the start.
If you decide to build one, you need to do a lot of reading here, and on other forums, and there are many other web pages giving advice.
Web searches for "DIY CNC Router", "Self Build CNC Router" are a good starting place.

Hope that helps a bit.

Cheers
Greeny

Great Photos, by the way!