I now see your Pace mower has the folding handle bars Owen, so if original it would be a Pace Special from 1959 to 1961, the Pace Special should also have a recoil starter so with a mower this old it's difficult to know what parts are original as the engine may have been swapped at some stage ,on the front of the top crankcase there shouldn't be a casting that reads Victa .
Yes the engine is a Victa 125cc 2 stroke as Victa bought out Pace mowers in 1959 but kept it a secret from most people then Victa closed Pace mowers in 1965 after which Victa just later on used the Pace name on Victa mowers.
A Victa engine on a Victa mower had Victa cast on the crank case but when Victa engines were used on other Mower brands the crank case had no trace of a Victa marking / casting name.
Mower ad below advertises a Pace Standard but is a Pace Special.
