D'oh, don't need to calculate the maximum line length (in $-) since it's known to be 82 for shape Saturn. That, plus some routine whittling has reduced the golf score by 39 strokes down to 452.

sub I{s-^-$"x$_[1]-gem;$/x$_[0].$_.$/}
sub D{$~=shift;system($^O=~Win?CLS:"clear"),print,
select$Z,$Z,$Z,$~for@_}
sub R{$i=0;join$/,map{$j=0;join"",grep!($j++%$_[0]),/./g}
grep!($i++%$_[0]),@:}
$S=join"",@:=<DATA>;chop@:;
$_.=$"x-(y---c-82)for@:;
D.3,@X=(I(20,41,$_="."),I(20,41,$_=O),I(15,31,$_=R 4),
I(13,28,$_=R 3),I(10,20,$_=R 2),$S);
D.2,(map{$n=$_;join($/,map$_ x$n,R($_)=~/.+/g,"")x$_}2..4)
[0..2,1,0];
D.1,$S,join"",map+reverse.$/,@:for$%..5;D.3,reverse@X
[download]

Update: Down to 437 now. There must be more there, let's see if thospel or mtve can beat this by 100 strokes. :-)

sub I{$x=pop;$x=~s-^-$"x$_[1]-gem;$/x$_[0].$x.$/}
sub D{$~=shift;system($^O=~Win?CLS:"clear"),print,
select$Z,$Z,$Z,$~for@_}
sub R{$i=0;join$/,map{$j=0;join"",grep!($j++%$_[0]),/./g}
grep!($i++%$_[0]),@:}
$S=join"",@:=<DATA>;
chop,$_.=$"x-(y---c-82)for@:;
D.3,@X=(map(I(20,41,$_),".",O),I(15,31,R 4),
I(13,28,R 3),I(10,20,R 2),$S);
D.2,map{$n=$_;join($/,map$_ x$n,R($_)=~/.+/g,"")x$_}2..4,3,2;
D.1,$S,join"",map+reverse.$/,@:for$%..5;D.3,reverse@X
[download]

Still chipping away... 425

sub I{$x=pop;$x=~s-^-$"x$_[1]-gem;$/x$_[0].$x.$/}
sub D{system$^O=~Win?CLS:"clear";print;select$Z,$Z,$Z,pop}
sub R{$i=0;join$/,map{$j=0;join"",grep!($j++%$_[0]),/./g}
grep!($i++%$_[0]),@:}
$S=join"",@:=<DATA>;
chop,$_.=$"x-(y---c-82)for@:;
D.3for@X=(map(I(20,41,$_),".",O),I(15,31,R 4),
I(13,28,R 3),I(10,20,R 2),$S);
for$n(2..4,3,2){$_=join($/,map$_ x$n,R($n)=~/.+/g,"")x$n;D.2}
D.1for($S,join"",map+reverse.$/,@:)x6;
D.3for+reverse@X
[download]