What a lucky man you are to have your grandfather’s plane.
I just joined the site so you are probably finished with your restoration. I have to agree with the Evapo-Rust recommendation, an amazing product, safe, no fumes and one quart can be used over and over for rust removal till it is black and no longer works. It will remove paint so I only use it for metal parts. There is an international distributor in Ireland, closest to you, their website has a list.