The 4th car WILL have an engine, plus a toilet, and extra luggage space, and an estimate of 50 - 55 seats
The entry into service is not known currently, and is subject to a few final approvals from the DFT but is hoped to have them done for the start of the December timetable.
This will give us 20 x 4car and 31 x 3 car sets.
2) We have only 2 class 158s left! They are 158772 / 158774.
They should be gone by June at the latest.
Anyway, when I get more info on the above ill let you know.