If you do not have, you can buy a 1L two stroke mixing bottle. I would suggest you use this for the line trimmer.
Or buy two and label them and use one for the trimmer and one for the mower.
Then the fuel in your can is ULP (or 95) and if it gets too old you can put it in a car. (not that you cant put premix in a car, done that before)
Run the mower on 25:1.
The whole Valvoline and 50:1 is ok for Victas thing is a marketing scam.
I would imagine that the tech people at Victa had the biggest bun fight over that with the marketing department.
The hardest thing with rebuilding the motor is getting the crank pin undone.
Plenty of info on the forum here.
Cheers, Bob.