What did your replacement diff come from? Surely someone knows.

If this replacement diff has a larger pinion thread & a much larger yoke bolt pattern on a circular flange, then my money says it's an H150.
They are a good diff, but they need a little extra to enable them to be used in an H145 axle housing.
Extra= spacer, gaskets, & suitable tailshaft with the larger uni joint yoke.

I recently sourced a tailshaft from a Sunny wagon & measured it against my Daqtsun 1000 shaft to discover that they were exactly the same length. The only fly in the ointment could possibly be if the flange of the H150 is further forward [towards the gearbox] than the H145 which would necessitate a shortened tailshaft if the difference is significant. If it is only a poofteenth different, then there should be enough movement in the slip joint at the gearbox end to accomodate it, & the sliding yoke on the Sunny shaft, which went into a 60 series gearbox, will fit the smaller 56 series gearbox.