I took the block to the machine shop to be measured today. The outcome was that number 5 bore is too badly corroded to even be able to fit 60 thou oversized pistons. However it’s not all bad news, the other 5 bores are in good condition. My 20 thou pistons can be re-used with a new set of rings and the machine shop has said it is possible to fit a liner in number 5 bore. I’ve decided this will be the best option as even if I source a second hand engine there is no guarantee what condition it will be in so I could still be faced with a scrap block or the cost of a rebuild this anyway.