perl -V (note upper case V) displays a lot of useful data, which you can report on individually...

• perl -V:archname will tell you if it's a 32 or 64bit perl program.
• perl -V:ivsize if this outputs 8 perl can use 64bit integers, if 4 32bit.
• perl -V:ptrsize if this outputs 4 your perl uses 32bit pointers, if 8 64bit.

To use perlbrew to install a 64bit perl do perlbrew --64all install perlversionhere.