u need 46t spur or to raise the diff by 2mm using diff spacers - Kyosho Center Diff Mount Spare (ST-R)
[KYOIS054]
u need to dremel the chassis a bit. done in on my 5t and now 6T see it here
Thanks.
I have tried the spacer method and 2.5mm is just sufficient.
The 50T spur gear hits the top plate of diff mount, too.
I hope 46T derlin spur gears back in stock soon.