Take a look at my Bacchus website in the Projects area and scan for repair of Hull / Deck Joint.
I tried to sketch and summarize what I found and repaired. It also includes links to some other worthwhile sites w/ actually as l MS photos that I found helpful.
Happy to answer any specific questions. There are others here on TF that have tackled this job.
Also other threads about this I believe in the Marlow MS builders section