That’s a lot of modification, almost every part would need to be changed. And not just for the size but also because you have those x y pipes in the same z plane. That would cause interference between the x and y gantry bars. If you overcame that I feel it would still have a huge negative impact on your ability to tram the machine and on the cores ability to withstand horizontal forces.
I strongly recommend building the machine stock first, then decide if it needs to be changed for your uses. I have seen mpcnc as big as 24" X 36"… if you want bigger than that build a lowrider 