Extending a Range 50a line Matching Wire?
Completely unusable.  It was installed illegally from the start, and it’s illegal even if you didn’t move the range.
Once upon a time (prior to the mid 1990s) it was legal to install a range with certain special 3-wire cables. You could never have used /2+ground cable.   You could have used:

Cable with an insulated white neutral (i.e. /3 no ground).  But of course that quickly went extinct after grounding started to be required in the 1960s.
SE cable specifically, which is made for service entrances, and has a “meshed” bare conductor which is actually designed to be neutral.  However that stopped having a reason to exist in #8/#6 after power companies stopped offering 60A service and set 100A as minimum.

NFPA’s purpose was to allow suppliers to use up their old stock of the above cables... and after that, everyone would be forced to use /3+ground.  Well, some installers thought that gave them permission to use /2+ground.  They were wrong.
Not least, the ground wire is too small to be safe as a neutral.
So the whole homerun needs to be dropped in the dust-bin, and re-run from scratch with proper wire.
You can run it in aluminum if you really, really want to... that’s not the issue... but it has to be /3+ground, and it has to be a 4-wire connection. You have no grandfathering and it must be done to modern spec.