G'day all,
Yep, a 'bitsa' for sure.
Having at last had a chance to look up the Victa Model Info listings, I'd say it's a 1968-9 Model 560 New Utility 160 motor and cowling [assuming it actually is a 160], fitted with a 125cc 'round torpedo' muffler, on a Model 530 [or earlier] Utility base.
Maybe back as far as the Model 12 Ute - they didn't change much.
Yes, the rear wheels are indeed the 1950s 'Victa 18 type', and are somewhat in demand by Victa 18 restorers, these days.