My boat lost a bit of draught on the website to "fit" through the Ribble Link booking. The rotating sea lock (the pinch point) was fine.
If you're worried, book for a higher predicted tide - they run uphill from about 8.6m to 9.5m - and try and get out of Tarleton as early as possible or give it more beans down the Douglas.
Basically you'll be fine.
Unless you're tail end Charlie on a low tide, in which case you'd want to divert to Preston Docks and go up the link the day after, which is the fallback plan if it all goes wonky. I'd actually recommend adding this in if it's the first time you've done the Ribble Link, simply because most boats don't do it, and it's there!
They'll make a special exception for you now you've said that and close them in July, which is a shame because I was thinking of doing the Rochdale this year...
Maybe I'll go in June instead! 🤣