The class 143 is a varient of the pacer train that ran until 2021. It served the same services as the class 150 on West Cornwall local, so it would fit right in on this route. The trains were infamous for the bus doors and deafening flange squeal. They had a top speed of 75mph.
They didn't actually run on this route - during the 1990's when the route is set the Class 143 fleet was primarily based at Heaton depot in Newcastle operating local services including on the Tees Valley Line. They were later sent down south to Cardiff and Bristol/Exeter, and the ones that ended up with FGW/GWR very rarely went further west than Newton Abbot/Paignton as far as I understand. Something like a Class 153 would be more appropriate.
In the first decade of their lives, the Class 143 units were based in North East England. They would be a better fit on Tees Valley Line I think.
OK, you probably know better than I do considering my main field of expertise is London and the southeast where it live.
I believe a couple of 143s made it down to Penzance in Wessex days - one had a Kernow Sticker on the front after it's vistit. They are banned from the branches, and are very restricted on the Mainline, so if one ever did make it that far west it would be sent back ASAP. 142s were tried on the branches in the 80s but as they were having to have new wheelsets every 3 months they were quickly removed
