I have pulled a cosworth T34 and XR4Ti T34 apart and checked them out, so far all have been the same sizes / wheels. The difference was in the housings only. I had checked on exchange / refurbish kits and found as Tabetha said that the T3X units all had the same inner section... I found that you can pull the housings off easily and peek around without fear of damaging anything and it demystifies a lot... Don't undo the nut on the turbine shaft at all as it would effect the balance As for the wheel size that would be the case from T3X to T4.