Yes, you need to know the exact compilation configuration of your old Perl version. perl -V usually outputs most of what is needed, but there may be differences in how your C compiler (now) creates code.

There is no way to determine what Perl version a module was compiled for after the fact. I suggest naming the directory extlib-5.26.0 (or whatever) to keep track of things.

Most likely you want to read the Coexistence with earlier versions of Perl section of the installation documentation of Perl.