Just change the entire for loop to this:

foreach (qw(0 3 8 20)) {
               my ($word2) = split(/ /, $lines2[$_]);
               my ($word3) = split(/ /, $lines3[$_]);
               print "$lines1[$_]:$word2:$word3\n";
       }
[download]

Just substitute the desired line numbers (each one -1, remember) inside qw(). If you do have large data files, use gryng's method below.

To grying: sorry for making you gag, I am studying your method closely to make up for it.