i run a straitline on my enduro. no roller just moto-style slider with a top guide and bash. If you're using a clutch rear mech you could just go with a top guide from mrp or similar if you don't normally worry about rock strikes, or edges and ledges to hang your bb on.
if ya find yourself in a hurry you're probably not that important
I have a 5mm or so spacer on mine. When I fitted mine, I had to get Specialized to send me a new adapter (the bit that originally bolts between the derailleur and the frame. I think the spacer came with this, but some washers should work. Hope this helps!