future hybrid, but some?'s

I'am brand loyal and would be doing a 250r to crf450 conv. One question i have is the tranny in the crf. Aren't the gears in the crf a tad bit narrow when compared to the trx450? So putting them in a quad for extented time will eventually fail? Would it be better to buy a hybrid frame from someone like walsh, lonestar, or using a stock frame pretty easy to setup.(Don't race) What are the other cost you guys with 250rs running into? Like you can't use a trx radiator, expensive exhaust, air box, possibly rear suspension setup? thanks for any info I don't have my heart set on building one just kicking the idea around.

I've heard the gears are more narrow, but have never heard of any problems like gear failure etc. They are definatley taller, I can tell you that.
An aftermarket frame is the way to go! Much less motor mount cracking, You dont have to make the mounts, they're lighter, and an aftermarket frame will always handle better. But you don't race so it's probably not a big deal.
My problems are exhaust and intake right now, the usual.