You can make pretty much all of the VSR cylinder guts with a lathe. Plenty of people have made new pistons and spring guides themselves. Making a new cylinder will require boring out the receiver and making new cylinder guid rings
If you get a tube of the same spec then you'd not really be winning anything TBH- Well cylinders are tighter than VSR ones and there's not point in replacing it with the same thing. Piston can be made out of any of those-Aluminium is easier to work with and a more popular option.
It's pretty simple. Marui Spec VSR cylinder is 23mm wide. WELL is 21~20mm wide (Depends on QC and batch). Well's is smaller,and so is the receiver and cylinder guide rings to support the smaller cylinder.
Parts compatibility is more of an issue. It's still got enough volume to function perfectly but Joule creeo won't be as profound as like on,say,a TM Gspec(Which is just absurdly overvolumed)