How is the 5.6 to 5.8 migration process

Hi- I have been putting off migrating a very large 5.6 site to 5.8. The site includes a lot of custom blocks and a ton of pages/content/images. Has anyone migrated a site with custom blocks? Assuming I successfully recoding the blocks in 5.8 -- does the migration tool do a good job with moving the pages including custom blocks?
Is there a good sources that summarizes the differences between creating a custom block in 5.6 vs 5.8? Any good examples showing what a contoller.php file looked like in 5.6 and how it was changed to work in 5.8? Any suggests for removing some of the pain from this process is greatly appreciated.

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hutman replied on at Permalink Reply
The process is still quite painful but if you create all of the same blocks with all of the same fields you should be able to import them.

The process for creating blocks for 5.6 is very similar to 5.8, you will need to namespace your controller.php, you will need to make sure that all of your block names are not camel cased, and the db.xml file changed slightly (old: new: ), but other than that it's basically the same. There are quite a few free blocks on the marketplace that you can download if you need examples.