What about Date::Parse?
Update: Do you negitive numbers for dates before 1970?
Update: I did a little testing of this and it won't work for your needs. Sorry for the bum suggestion. Oddly enough it will give you answers for dates before 1970 if that helps.

 
#/usr/bin/perl -w
use strict;
use Date::Parse;

my $date;
$date = "Aug, 20 1955 11:09:55 +0100";
my $time;
$time = str2time($date);
print " $date\n";
print " $time\n"

# perl tmp.pl
 Aug, 20 1955 11:09:55 +0100
 -453390605
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Josh