Love it!. Its not pre 56, So you may keep your life Lol. smile
Its running the Villiers midget 98cc making it an early model 1 Code, it would be a 1V98.
The odd thing is, the first Mk 3 came with the fuel tank on the cowl,this clearly does not,either way its an early model and a gem of a mower,pull the cowl off sometime and check the date code on the flywheel, I'm guessing it will be 1956, simply because it retains its early handle bar tank set up and not on the cowl making it maybe slightly later.

Ok, if your careful, gently clean the surrounding area of the tank where the decal would run, sample sections periodically for whats being removed then proceed with water, then metholated spirits, then turps. No scrubbing or brushing just wipe it over with a rag until you see how the remains react. When its clean assess whats left under the rust dust and grime,turps will darken what is left and often an old decal is etched into the metal,you may be able to trace the remaining letters onto some paper and replicate that way.
I've done this many times on Cyclops toys and pedal cars and the occasional mower...maybe this will help.

Really awesome mower you have Gizmo,wish I had one...I do have an engine though, lols.