my @transformed = map +{
    map {
        my $k = delete $_->{ACC};
        $k => $_;
    } @$_
}, $data1, $data2;

my @merged;
for my $key (keys %{ $transformed[0] }) {
    if (exists $transformed[1]{$key}) {
        push @merged, { ACC => $key,
                        %{ $transformed[0]{$key} },
                        %{ $transformed[1]{$key} }
                      };
    }
}

print Dumper \@merged;