If you have the Save Cass Mod you can still complete both quests. Get the evidence against the Van Graffs and Crimson Caravan company, but do not tell Cass about it or go to Ranger Jackson. Then complete the Birds of a Feather quest as you normally would, then give the evidence to Ranger Jackson, completing Heartache by the Number. When you travel back to Freeside the Van Graffs will be hostile, but if you kill Simon and the Silver Rush Crier you can still move around Freeside freely.