... re-join the fields in the middle, possibly distorting the white space.

I, too, wondered about the significance of embedded whitespace in the  FROM field of the data and about the fixed-field nature of the data, concerning all of which zBernie is silent in the OP and, to this moment, elsewhere in this thread. If embedded whitespace in the  FROM field matters, it's simple enough to deal with it using split if the sub-strings corresponding to the separators are also captured and everything is re-assembled with a minor modification to your existing split approach. (Even so, I think I prefer a regex-based extraction approach like that of davido, which lends itself better to data validation efforts.)

>perl -wMstrict -le
"my @data = (
   'REQID     DEST             FROM                     DATE   TIME   
+ nPages  RCV',
   '138454  mail_room     Marco`s  Pizza        12/26 21:52    1  rcv'
+,
   '138446  custsvc      973   618    0577     12/26 18:44    1  rcv',
   '138445  county2       spam                  12/26 18:41    3  rcv'
+,
   '138444  custsvc      spam                  12/26 18:30    1  rcv',
   '138439  county2       7182737253            12/26 17:54    2  rcv'
+,
   '138438  county2       Acme Products, Inc.   12/26 17:52    1  rcv'
+,
   );
 ;;
 for my $record (@data) {
   my @fields = split /(\s+)/, $record;
   my $from = join '', splice @fields, 4, $#fields - 11;
   my ($reqid, $dest, $date, $time, $pages, $rcv) =
     @fields[ 0, 2, map { $#fields - $_ } 6, 4, 2, 0 ];
   printf qq{'%s' \n},
     join '|', $reqid, $dest, $from, $date, $time, $pages, $rcv;
   }
"
'REQID|DEST|FROM|DATE|TIME|nPages|RCV'
'138454|mail_room|Marco`s  Pizza|12/26|21:52|1|rcv'
'138446|custsvc|973   618    0577|12/26|18:44|1|rcv'
'138445|county2|spam|12/26|18:41|3|rcv'
'138444|custsvc|spam|12/26|18:30|1|rcv'
'138439|county2|7182737253|12/26|17:54|2|rcv'
'138438|county2|Acme Products, Inc.|12/26|17:52|1|rcv'
[download]