Thanks very much for that.
I was in the area last week and got a look at the bus timetables. The buses seem to have improved somewhat.
There is an Hourly Bus from Taunton to Yeovil now
, the train service never even made two hourly properly, perhaps if it had become hourly it would still be running.
The bus runs via Langport, Somerton and Ilchester to Yeovil Bus Station which is I think pretty close to the old town station.
Of course if you want to go on to Yeovil Junction from the bus station then you have to change buses and get the separate half hourly shuttle to Yeovil Junction station.
Some things never change
Montacute etc. get a two hourly local bus service to Yeovil but not to Taunton.
Your father is right about Pen Mill although it wasnt a southern station. Pen Mill is on the ex Great Western route from Westbury to Weymouth and some taunton trains did run through to Pen Mill.
There is a track from Pen Mill to Junction but no passenger trains run between them. It is used as a diversionary route for expresses from Paddington when the line via taunton is shut.
There is a plan for all westbury - weymouth trains to run in and out of the disused platforms at Yeovil junction but whether it ever happens remains to be seen.