This has now been tidied up and built with my single speed kit from my previous elevated chain stay commuter and a salsa fork. I suspect the plate was added after the seat post was out too far and there may have been some cracking. Seems strong enough so far and I am running a 400mm post well inserted into it. I shall add some photographs when I am out on it in the sun.
These frames do ride very nicely, so hopefully the repair will hold, this is just going to be a work bike so I am quite hopeful it will last