I have found the proper OEM wheels for this frame, on the All Mower Spares website.

They are:
- Victa 6 Inch Supatrak Wheel Assy 150mm CH87081G AUD 27.50
- Victa 7 Inch Supatrak Wheel Assy 175mm CH87082G AUD 30.50

Not cheap! I won't be doing that right now.

Replacing the frame bolts in grade 304 stainless steel requires:
- Coachbolt (aka cup head square neck bolt) 5/16 UNC x 1.75" or M8 x 50mm (4 off) (replaces HA20310D)
- Nyloc nut 5/16 UNC or M8 (4 off) (replaces HA24845D)
- Flat washer 1/4 x 3/4 x 18 gauge or M8 x 17.0 x 1.2 (4 off) (replaces HA22241D)
- Hex head flange bolt 1/4" x 3/4" or M6 x 20mm (4 off) (replaces HA21073D) (or else use e.g. M6 hex bolts and M6 x 12.5 washers)
- Nyloc nut 1/4 UNC or M6 (4 off) (replaces HA24844D)

UNC for authenticity, or else metric or BSW. Depends on your spanners really - I like metric. That's just over $10 worth of new fasteners. Postage $13 extra if you buy online - I might think of more stuff I need to make more use of the postage cost.