Good luck on exhaust. Thats been my major issue on finishing my LTR based one. If you get on youtube there is a European rider that has one like yours set up for MX with good results. The amount of fab work to make it work in a YFZ is a whole lot less hassle than the LTR set up which is definately a plus! I actually had mine in a YFZ at first then pulled the plug on it after I aquired some more LTR chassis parts. I'm not trying to dampen your spirits or bash your build at all but you're definitely going to need to make some antivibe motor mounts and gusset the YFZ frame up, they are prone to cracking around the welds and subframe racing MX. I MX'd the YFZ's for 3 years and when I finally made the switch to Suzuki I tore the YFZ's down to PC and sell and found 37 cracks combined on the main frames of my 2 race bikes. Best of luck!
Cool thanks for letting me know. Any chance you could help me out a bit since you've already built one and worked out the faults? Like what radiator to use or where you think those gussets should go? It almost looks like an aaen pipe would make it in there nicely. Don't know if you've seen this but it's what put me off using the ltr frame (and I couldn't afford one)
http://www.ltr450hq.com/forums/suspension-steering-chassis/3172-frame-cracks-swingarm-cracks.html ...but yeah, the yfz frame does look a lot weaker and it could be worse for cracking.