Is it the version of perl that I run "perl Makefile.PL"

Yes.

Get the right "perl" and that's all you have to worry about. Simplest way to do that is to just spell it out. That is, if this 64-bit integer build of perl is in '/home/me/perl589_64int/' just run:

/home/me/perl589_64int/bin/perl Makefile.PL
make test
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and all should be sweet. Just remember to run 'make clean' before you try to rebuild the module using a different perl - or you'll likely get some confusing 'make test' results.

You might also like to build a perl with both long doubles and 64-bit ints (-Dusemorebits). 64-bit integers can be handled differently, depending upon whether long doubles are also available - so it's safest to have both options covered.

Update: Just to elaborate on what I meant by 64-bit integers can be handled differently (which is not strictly correct), consider this script:

use strict;
use warnings;

my $x = 2 ** 55;
my $y = $x + 1;

if($x == $y) {print "wow\n"}
else {print "as expected\n"}
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One would naively expect that, irrespective of whether perl was built with -Duse64bitint or with -Dusemorebits, the output of that script would be "as expected". But that's not so. The -Duse64bitint build outputs "wow", and the -Dusemorebits build outputs "as expected".

Cheers,
Rob