15x10 what backspace 69 cutlass

[69cutlassrkt]

I was thinking 6" backspace would be best for the rear. I think that's what backspace I have right now with the adapters and my 17x10.5 torq thrust Ms.
What do yall recommend?

Also billetspecialties no longer has 17x9.5 wheels available on their website. Know any wheel companies that sell a 17x9.5 or 18x9.5 5.5 backspacing front and a matching 15x10 rear wheel in correct back spacing and bolt pattern.

Thanks