@HeaderRecordNames   = qw/$RequestYear $RequestMonth $RequestDay $Requ
+estSequence $RecordType $RecordSequence $Record/;
@HeaderRecordLengths = qw/A2           A2            A2          A4   
+            A2          A2              A1486/;

...

my (@HeaderRecordNames) = unpack(@HeaderRecordLengths, $_);
my (@RecordNames[$Recordtype])=unpack(@RecordLengths[$RecordType]);
[download]

Try using an intermediate stage for the mapping of values.

@HeaderRecordNames   = qw/RequestYear RequestMonth RequestDay RequestS
+equence RecordType RecordSequence Record/;
$HeaderRecordLengths = q/A2A2A2A4A2A2A1486/;

...

my @head = unpack($HeaderRecordLengths, $_);
my %Header = map {$HeaderRecordNames[$_] => $head[$_]} (0..$#head);
my @data = unpack($RecordLengths[$head{RecordType}], $Header{Record});
my %Record = map {$RecordNames[$_] => $data[$_]} (0..$#data);
[download]

This should work and create a hash containing key => value pairs you are after for both the header and record.
Note: Untested
UnderMine