Looking good as always Jonathan. If I hadnt been late to the party, I'd also have suggested replacing the roof - it makes sense, as the detail on the kit one is wrong anyway
As regards rainstrips, some (in BR days at least, and possibly on BR built vans) most definitely were straight and parallel to the roof edge as you've fitted, although it wasnt the most common pattern; this is one of those things that many years ago I took fa -arr too much of an interest in and mentally logged any variation I came across in photo albums.
I take Mike's point about their possible effectiveness, but would cite the later BR standard vans in this connection, which had a straight 3-part strip with slight gaps. I would say that the most common pattern - and possibly your safest option, unless you understandably dont want to disturb things again - is a slightly longer (but still straight) strip which runs inwards from the corner at maybe 25 - 30 degrees, or the slightly arced pattern as on Mike's van
I've no idea what the LNER GA shows (would this have been binding on the works anyway?) but I think every drawing I've ever seen shows the very sharply curved strips like those on the kit mouldings - I've never seen any photographic evidence of this and I feel it must be very unlikely as it just wouldnt be possible to get the batten into that shape without specialised forming processes, which I wouldnt have thought would be worthwhile