It may well be worth the $25K but I just think it smells a bit. 31,000miles over 40 years is only 775 per year. I only drive mine on 1 out of every 4 weekends and I think I would do that in 10 years. Particularly in Cowra you only have to go to the next town and back and you've done 100.
Plus the question has to be asked why would someone who hardly drives the car bother to do an engine upgrade?
Having said all that even if its done 131,000 miles it might still be worth $25,000 if it is in good enough condition.