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.
always talk to your bike and thank it when it gets ya home safe
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!