Was looking thru some old threads and found this and figured I should put some kind of closure to it since I'm the one that started it.
Well, it took 4 years, but I finally did the 440 kit from Thumper Racing. Taking into account everything I learned in this thread, I kept the stock cam and had Kibblewhite valves installed during a valve job. Also replaced the camchian for good measure. As discussed, temps did go up significantly, 30*-40*F oil temps that is, even with running the cooler DPR9Z plug. Wrapping the header tho, dropped temps back to pre- 440 levels.
Since doing the 440 kit a little over a month ago, I have installed the Mikuni pumper and I have to agree with XRs Only, this "is" the carb that "should have been" on the XR.
I also installed a Hebo hydraulic clutch to offset the difficult lever pull from the heavy duty clutch springs that were part of the 440 kit.
Now I'm considering an exhaust can. I don't want it loud, yet it should have better flow and performance than my Gordo modded stock can. Looking at the WB E Series and the FMF Q.