Hey Polybus,

Yes,Mowers one and three are both Model 5 series 3.
Mower 2 since weve seen the Images and serial is a Model 4 STD.
The example on ebay is as youve stated a correct Model 5 Series 1.

As you go along through the various forums you will learn the differences between all the models as the information here is very concise and proven accurate in almost all aspects...

A quick run down on the model 4 Automatic . It was released in 1957 and was supposed to revolutionise mowing as we know it...but unfortunately and very quickly it proved to be unreliable and was discontinued. Your mower example is what is left of this iconic release. The parts from the Automatic were deleted....(This setup was called the Predicta system) This link to the Auto thread will explain everything.

https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=47929.

So your model is what remains of the automatic,A std Model 4 with no Predicta setup. And it appears correct as sold with correct serial no.
My point with the cap and cowl is really quite simple. The use of a metal fuel cap would generally not be considered a fittment for a mower this late,and more suited to the models id stated,BUT I have seen some odd examples.
My point in the post was merely this and i came up with the same conclusion you did....that the cap tank cowl and base all seemed to be a colour match,and was probably sold the way we see it now,with the exception of the starter off course.:) So while its minor it is something different. and in my opinion it should be restored the way it stands,same cap and sticker position:)

So the model 4 STD is basically the fill in model after the Auto failed and the Model 5 S1 started....The first Victa Special.Which again is the one in the ebay link you showed.

Anyways you will learn a lot as you go along be patient and ask anything you like and we will have an answer for you smile enjoy your resto's and I cant wait to see the model 4 as its one of my favourites:)