Hi Mark what you have found is the difference's in age.As I had brought to the forums attention in this post.
https://www.outdoorking-forum.com.au/forum/u...amp;Main=6267&Number=29763#Post29763
Check it out it will help a little.
The one still in the crankcase is an earlier version of the 160cc crank the other is the later model.Neither will fit each others crankcases as if you look they will have different shafts on them.If you have a look at the numbers on the crank case you will see there should be a difference in years.The one in the crankcase should be (From Memory,so don't get upset if I'm wrong) pre 1974 the other should be after that.If you could stick the engine numbers up I'll be happy to verify that.

Here for a good time,not a long time.