I've just been on holiday in Cornwall and took myself off to Port Isaac to see what I could find (now I know I'm a FH-anatic

According to some locals, there has never been a burial place in Port Isaac itself - there isn't enough room. All burials have been in St Endellion churchyard, a couple of miles inland.
There were two Methodist Chapels in Port Isaac, both now out of use. The Wesleyan Methodist Chapel in Middle Street appears to be a private house. The United Wesleyan Methodist Free Church is now a pottery, but a lot of the interior seems to be unaltered - see picture at the bottom of
www.portisaacpottery.co.ukI carried on to St Endellion churchyard to have a look round, but with limited time and a very hot day I couldn't find the grave you mentioned. There doesn't seem to be a separate area for Non-Conformist burials, but there are graves dating from the early 1800s to present day.
Can I suggest that you ask the elderly gentleman if he can at least remember exactly where the
graveyard was, as this might help someone else.
Sorry I couldn't do more - I would love to have solved this one

Linda