Cannot get trans & clutch housing connected

[FarmallM51]

Lowering clutch housing onto transmission but cannot get drive shaft needle bearing to completely slide over transmission gear shaft. Lacks about 1/2" of completely sliding together. Any ideas on what could be obstructing this? Needle bearings are all in place & no debris in bearing housing, shaft & bearing lubed with synthetic oil. Thanks.

[Sdexta62mi]

Did it come apart difficult? Maybe there is some corrosion on the dowel pins or a bad spot on a dowel preventing assembly.