i need some help

[revmopar]

I installed an LS2/t56 combo from a 2006 gto into a 67 gto and there is a rattle that I am trying to daignose in the engine, I found this youtube vid with the exact noise (not the car I am working on but the same noise) can anyone tell me what this is?
https://www.youtube.com/watch?v=BB13b9ot6dA

Thanks in advance