Pete, need more description in your posts on what you are working on and pertaining to. It's hard to remember all of a single guys posts here.
That said, what ARE you working on? If you have a tork tube, the trans will need to be changed to open line type too and diff rear. If you go to the "archives" and search or the "tech" articles on the main page, lots has been said on these two items. Finding a 55-1 first series will get you an open rear and trans that will just bolt in. Kinda rare to find, specially in New Z I would think. This is assuming you have an AD 48-54. What DO you have and what size? 3/4-tons or one-tons with 4spds are usually all open drive too, even back in the older ones.
