My B10 parts book shows three part numbers.

13035- 18000 Assy-cover Timing chain. [to E/# A10-184227] [This is for the earliest engines with the single row timing chain]
13035- 18001 Assy-cover Timing chain. [from E/# A10-184228] [duplex timing chain] Not interchangeable with former.
13035- H1000 Assy-cover Timing chain. Interchangeable with previous unit, but not the first.

Two part numbers for the Datsun 1200.
13035- 18001 Assy-cover Timing chain [Up to 04/70]
13035- H1000 Assy-cover Timing chain [From 05/70] [Interchangeable with former part No.]

Note that these two numbers match the last two numbers for the A10 engine.

The earliest A10 engines used a single row timing chain with its own timing case. When they switched to the duplex chain, the timing case was also changed & this one had a guide for the chain.
The replacement timing case, from 05/70, deleted this guide as it was found to be un-necessary.

So yes, Matto1kUte is right, there were basically two non interchangeable timing cases.
One for the single row timing chain in early 1967 models &
One [in two versions] for the duplex timing chain.

The entire duplex timing chain, sprockets, hydraulic adjuster & timing case from the later model engine is interchangeable with the early. single row type as a complete assembly.