It had the extra ventral fuel pack, plus the fitted they over wing tanks, and they replaced the radar with a fresnel lens to improve the radar signature for the students. It would routinely stay on station whilst 2-3 students flew successive sorties against it.
though one Irishman had to declare a Mayday and divert. One of the student sorties delayed and delayed and delayed whilst he held admiring the sky until after one routine Pigeons check he asked for a repeat and diverted to the nearest suitable runway (Linton on Ouse?, long time ago....)