G'day
LRT, and a warm welcome to the ODK Forums.
From that model number, it's 86-87 year of manufacture; it's actually the 'Pro 550 Self Propelled' model. One of the very last of the full-crankshaft Victas; most of the model range had gone to the half-crankshaft PowerTorque engine by then. So it's the original engine I'd say, and no, a PowerTorque won't fit it.
Most parts are still available for this one, with the exception of the decompressor valve assembly. However, if that one has three clips holding the diaphragm chamber together, rebuild kits are available, e.g.
HERE.
Piston rings are available in standard and three oversizes. That said, it's fairly rare for Victa 160's to get away with rings only when they're worn; the bores tend to wear oval, and they need to be rebored.
The basic service info on the engine and carby is available in the numbered sections
HERE as free downloads; the lower 'Attachments' docos require a paid subscription for access.
This engine has electronic ignition; if it has the separate electronic module, the problem could lie in either the coil or the module.
