extended shift lever?????

What I would do is go on Ebay and have a look at old YZ and IT shift levers.
You can get what you want pretty cheap and they all fit.
If not sure just ask the seller to measure it.
I run my old 74' shifter on the 400 in my Blasty and the 400 shifter in my 175 lol
 
I'll measure the distance between the peg and lever on a ltr450 and see how much longer that would be on a blaster. The 450's have a perfect length. If it's outrageous I'll start smaller.