Hey @Neil-Hodges ,
I’m not sure whether Migrations works for a v13→16 migration, but we’ve been using uSync Migrations for an in-place migration on v13 sites. It’ll cover off the Nested Content → Block list and Grid → Block Grid but it’s also a great framework to build custom migrators too.
Once you’ve done an in-place migration, you can then upgrade your site to v16 (although, as an aside, my experience is that v17 is already a lot more stable than v16!) as Owain suggests you’d do with his tool.
Owain’s tool is also a great option. Check which properties each tool will convert for you by default and factor in if you have existing experience of uSync Migrations.