From my experience LHD or RHD makes difference only if someone is really into RHD. They aren't daily drivers (at least majority of them) so it doesn't bother people. Facts are: small bits on your dad's car all adds up and small bubble of rust (even if only one) plust touch up (even if only one) is more expensive to get rid of than it is worth. So if you will take into account all "small" expencies and small bits to do it makes value of your dad's car lower. Especialy when you put it up for sale on a club forum where all of us know these small cans quite well.
I don't know anything about mechanical condition, but again, from my experience even 2 weeks without regular use makes a difference for them

So PLEASE don't take if hard - me and others are just trying to give you a real point of view. I wish you £2000 for it if someone will be happy to pay.
We all doing our best here for everyone who is new to understand fully what is going on. I am here just for a year but trust me - being polish I thought I ate all knowledge and I didn't. Have learned a lot.
So feel free to discus anything but try stay calm