Yes the T4S Lounge is after the passport control, go up the escalators and it's on the left side inside the duty free area.
If you want to take the IB3166 with the flat bed you won't have time to use the Lounge with the 55 min connection, but there are 4 or 5 later flights to LHR if you want to enjoy the Lounge. Bare in mind that at that time of the day however, you might be between the Lunch and Dinner service and the food offerings are more limited (I was there on Monday around 5pm and the Dinner service was not until 8pm onwards).