Here's another approach. It doesn't extract all the fields in one swell foop (the patterns I'm calling  $real numbers have to be extracted in a separate step), but one can imagine some degree of customization is possible for different types of records:

c:\@Work\Perl\monks>perl -wMstrict -le
"my @lines = (
   'C31 6  3 2.4 1.5 2.6  ',
   'C32 2  7 3 1.0  ',
   'H31 1 1 0 21.0 11.2 5.3 1.4',
   'T11 2  1 0 6.0 1.1 2.2',
   'L06 1  1 0 1.0 3.3',
   'L99 1  1 0 1.1 2.2 3.3 4.4 5.5',
   );
 ;;
 my $int    = qr{ (?<! \d) \d+ (?! \d) }xms;
 my $real   = qr{ $int [.] $int }xms;
 my $header = qr{ [[:upper:]] \d\d }xms;
 ;;
 my $n = 4;
 my $extract = qr{
   ($header) \s+ ($int) \s+ ($int) \s+ ($int)  ((?: \s+ $real){1,$n}) 
+\s*
   }xms;
 ;;
 for my $line (@lines) {
   printf qq{'$line' -> };
   my $got = my ($h, $d1, $d2, $d3, $r) = $line =~ m{ \A $extract \z }
+xms;
   ;;
   if ($got) {
     my @reals = $r =~ m{ $real }xmsg;
     print qq{'$h' '$d1' '$d2' '$d3' (@reals)};
     }
   else {
     print 'unknown';
     }
   }
"
'C31 6  3 2.4 1.5 2.6  ' -> unknown
'C32 2  7 3 1.0  ' -> 'C32' '2' '7' '3' (1.0)
'H31 1 1 0 21.0 11.2 5.3 1.4' -> 'H31' '1' '1' '0' (21.0 11.2 5.3 1.4)
'T11 2  1 0 6.0 1.1 2.2' -> 'T11' '2' '1' '0' (6.0 1.1 2.2)
'L06 1  1 0 1.0 3.3' -> 'L06' '1' '1' '0' (1.0 3.3)
'L99 1  1 0 1.1 2.2 3.3 4.4 5.5' -> unknown
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Update: Tested under Perl versions 5.14.4 and 5.8.9.