The high output ballast cleaning machines are absolutely ideal for track lowering but NR has mothballed them. They never got much use in Southern area as the level of cable disconnection is several times higher than even AC electrified areas due to the positive and negative cabling and impednace bonds. That said its still the best machine for track lowering.
Theres still one set operating on whatever LNW is called now. Having said that they're only good for track lowers if the underlying formation and subsoil is adequate as they can't install any sort of formation treatment. The Paisley Canal line had aggressive track lowers completed for the electrification project by the medium output cleaner (the HOBC's older cousin) and the ride quality along there is now suffering as the lowers removed the formation treatment between the former canal clay lining and the ballast with predictable results.