Thanks heaps Ian....Interesting all the 70's serials being so close.
For your reference,

17420 early model 2 tin wheel possibly using some model 1 parts...need to see more images.

60435 mid run model 2 tin wheel

The remaining are later rotomo model 2 plastic wheel.

Id like to see the complete 17,000 serial if thats ok and see what chassis and parts its running:) nice little collection.