According to the description, the riser cable is for PCI_E 3.
However, the 3070 is PCI _E 4
Should however work

I don't think it's possible just like that, because the 500DX has metal struts between the individual PCI panels. You'd probably have to bend them off.
I have both at home, if I get the chance I'll try it out and let you know again.

it depends on the case if you have enough space but because it is adjustable it should work :)