D-76 regular strength should have a capaticity of 10-12 films per 1 litre. That is 120 or 135-36 films. So 600 ml should be fine for 6-7 films, but after every 2 films a slight increase in developing time is recommended usually 15%. For more detail please refer to the instructions or Kodaks Datasheet on D-76. Disadvantage: you will have to keep track of the changes in time.(posted 8646 days ago)The alternative is to use D-76 diluted 1:1 one-shot(one part stock solution, one part water, one part would be 300 ml in your case). So you would need 300 ml stock solution for every two films. 600 ml stock would be turned into 1200 ml and would be fine for 2 times 2 films.( totals 4 films). The deloping time will be longer in diluted D-76.
As long as you do only 3 or 4 films at a time you may find it easier to use D-76 1:1. Some people prefer D 76 1:1 for the look, but that is up to you.
Regards,
Wolfram