I think some of the later model front bearing retainers (the part the throwout bearing slides on) have a lip seal included. The input shaft would need to have a smooth surface for the seal to ride on. I believe the earlier ones had an oil slinger up front instead of a seal. As long as everything bolts up and the shift linkage works OK, mixing and matching parts from different years will probably be OK. Just be sure all the parts move through their full range of motion without any interference. The synchronizer sleeve with the tapered collar and the squared-off one on the later assembly should interchange, as long as there's no mechanical interference with anything. Good luck!
Jerry

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