If its a vcd, tsunamiMPG encoder can associate these 2 streams into a single file one after another, from my memory.
Alsdo, no recompressing would be needed if they have the same format (actually, even if they arent but then they wouldnt be flawfree at decoding by hardware players and software players expecting vcd specs), so associating additionally wouldnt take a lot of time.
DAT files in VCDs are actual normal MPG files (just limited to VCD specs) so their extension can be changed to MPG for the associating process, then the output file's extension changed back to .DAT after its done.