Hi Dave,and Welcome :)Get some pics up and we can tell you exactly what it is:) For quick reference your engine no is located on the carby side on the upper half of the engine crankcase.
Also a single number digit(usually) on the lower half.This will determine at least what model the engine came of and if its original to your mower.There are no other numbers to Identify a victa 18,only the mower style/appearance.
But Images and the number together will make it much easier.
