Why not take advantage of the $/ variable like so

open(my $fh, $data_file) or die("ack: $!");
binmode($fh);

my @records;
{
  # see. the man perlvar for more info on $/
  local $/ = \4;
  push @records, [ $_, scalar <$fh> ] while <$fh>;
}
[download]

Now you'll have an array of arrays, where each array contains a pair of 4 byte records.
HTH

_________
broquaint