G'day Scott,
Welcome to the forum! I'm pretty new myself, but will pass on what I know. Both mowers look to be Victa "Special" model 5, version 1. The model five was made from 1957-61. As for which one to restore, the mower with the 285 engine number is probably the older, as the AA prefix engine probably comes from a later model. At least thats how I understand it, but there are plenty of guys on here that know loads more about engine numbers, than I.
As for paint, it is generally accepted that Model 5's were painted with hammertone paint in a colour called "Avocado". This was made by Galmet, but they discontinued the colour some time ago. You can still get 1 liter tins of Galmet Hammertone in gun metal, but finding a stockist can be tough. Best to call the company to find your closest retailer. and have it tinted up by your local paint store. The rep at Galmet headquaters claims the closest tint to match the original avocado green is tint code Dulux SS27 (for 1 litre of paint).
As for the handlebars, Wattle do a rattle cans of rust guard in a colour call Deep Brunswick Green. This is probably as close as you will come to the original colour scheme.
As for prepping the surface, sandblast followed by whatever takes your fancy. Both the above products can go straight onto metal I think, but whatever the label says would be best. Hope this helps
