Yeah or naah?
The frame I am considering is the SP cycle scale frame, could get good deal on a lefty XTR.

if you are asking if it will fit, then you need to look at the lefty's distance between top and bottom clamp.  as long as that is larger than your head tube then the fork will fit.    the forks are great and very supple so if you have a line on a good deal for a lefty i would recommend taking it.

thanks Jeff. Distance between clamps is 125mm, HT is 110 on the frame I am looking at so it should fit. only potential issue is that the scott has cable routing though HT, not on the side of the frame, so there is an adapter in there needing some room, not sure 15mm would be enough.

My first build 8-9 years ago was with a lefty:
http://chinertown.com/index.php/topic,811.msg8873.html#msg8873

I liked it, but had so many problems with it that I went for a no-maintenance Lauf for a year or two.
And finally switched to SID on all my recent builds

The helicoil failed.
I got a warranty replacement for the bottom part
And finally had an oil leak from the bottom tube.