Check out their website www.bbrmotorsports.com for more info. Their specialty is 4-strokes in aluminum frames. Why would you want a WR motor in a YZ frame? If the WR bottom end power characteristics or the YZ suspension is what you want, it is easier to make those changes with bolt-ons.
Their prices are very high because each bike is handmade. They do everything in-shop now, and have a in-house suspension and engine tech, 2 CNC machines, and all types of other equipment and supplies to do it right.
I may get to provide a full ride report on the 250F minibike soon . . . rumor has it they're building another one. Didn't get a chance to ride the last one, although it DID thunder past me at open practice a couple weeks ago. I'll give details as soon as I can get them. Look in the July issue of MSN for specs and Pete's impressions of riding the first 250F minibike, about 2-3 weeks.
I definatly love that cr250f, man that would be so sweet. But dude, the wr and the yz are so similar that you shouldnt switch motors. Get a banshee motor and see if they can house that in a cr's frame, that would definatly rip. I mean, except for the 2 huge exhaust pipes on each side.