Just in case you missed it in my earlier threads on IRS rear ends.

Ive studied tons of setups for a datsun and the cheapest and easiest for LSD is the
volvo de dion rear setup as it was based on upgrading the original leaf sprung design.

just needs your choice of independent diff, shortened driveshafts, volvo top frame,
driveshaft unis & brackets (can use disc brakes).
pics below show how simple it is just missing view of CV driveshafts.










The green circled highlights show where the driveshafts would go.
The green squared section is the top frame.
The di dion tube will need shortening for the 1000 but quite easy to do.