Posed a similar question yesterday to the helpful folks at Praxis.
My question was based in purchasing a FR219 from Flyxxi. The frame has a 68mm BB30 alloy shell. I was hoping to use some stripped down SLX cracks that have a 24mm spindle.
the answer from praxis was:
We do not make a Conversion BB for 68mm MTB frames.
Our 68mm is made for the 68mm Shimano Road cranks.
Our 73mm is made for the 73mm Shimano MTB cranks.
You can't put the Shimano MTB crank on our 68mm as our BB is not designed to be spaced.
In the NOTES tab we have a bullet point on this
• 68mm can only be used with road cranks. Cannot be spaced.
Sorry, at this time we cannot help you out.
instead i went with the Race Face Bottom Bracket BB30 for X-Type. appears to work with shimano cranks. purchased part from bikediscount.de
Hope this info helps. you may want to send praxis an email. they were very timely in a response.