The 4-CIG's (there was a CIG - class 421 in beta version around, I think by Michael Whiteley) ran on the Brighton - Hastings section. The older 4-CIG's made for Ultimate Trainz are on the DLS made by Mike 10. (Search for MB_4-CIG) 4-VEP's (Similar to the CIG's but with different window treatment). 4-CIG's/4-VEP's were sometimes coupled in multiple so you would get 8 car trains. You may even get a 4-BIG and a 4-CIG together (the 4-BIG had a buffet car). Sometimes a 4-SUB, or a 2-EPB or 2X2-EPB's may be coupled to a 4-VEP or 4-CIG unit. The beauty of Southern Railway EMU's was that they were mostly interchangeable and compatible. jayholland's outstanding SUBS and EPB's are readily available on the DLS in green livery, and I'm pretty sure someone will repaint them into BR Blue and BR Blue/Grey before too long!
The Hastings DEMU's ran mostly on the line between Hastings and Charing Cross via Tunbridge Wells (between Hastings and Tonbridge are the infamous narrow tunnels, the gauge of which either the contractor or the railway procurement officer got wrong. The upshot was that the builders refused to widen it without further payment and the Southern Railway had no more money to spend so had to construct trains of narrow profile thereafter. When third rail electrification became widespread across the Southern, there was insufficient clearance in the tunnel to allow it, hence the order for the "Hastings" DEMU units. Out of the 100 Class 33 Diesel locomotives built, 12 were built to "Hastings" profile.
The Hastings Unit is available on the DLS, although with black windows etc, it does lack the finer detail found on more recent models. When we had Trainz SP3, the detail of the Class 203 Hastings Unit was astounding!
http://en.wikipedia.org/wiki/British_Rail_Class_33
http://www.hastingsdiesels.co.uk/history/
In the 1970's, a Hastings DEMU Unit often worked the Saturdays only Brighton to Plymouth and return service - truncated at Exeter St Davids in the latter years. This working would have meant Hastings units sometimes worked the line between Hastings, Eastbourne and Brighton. Similarly, there was a summer Saturday service from Eastbourne to Cardiff often in the hands of a Hastings DEMU.
