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Head on over to Trail & Ultra Running Thread if you haven’t already. Lots of advice and experience in that thread dating back to the start of TT 2.0
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For flattish races, probably topping out a the distance you’re talking about, your marathon training principles will probably do you well. Clearly you won’t need the speed element, but it’ll all be about maintatining that efficiency. 4.30/km is a very steady pace for you, so it’s just about how long you can keep that form going for. That’s what you’ll need to work on.
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Personally, I think Ultra running deliberately veers away form the structure of the likes of a Jack Daniels. There is so much variation compared to ‘normal’ road races up to marathon distance - terrain, elevation, ground conditions, distance, weather, night vs day, self supported etc etc that writing a more formulaic style of book just wouldn’t work. I also think a lot of people, me included, head over in that direction again to deliberately move away from splits and miles and pace. It’s more about a holisitic management of body and mind (without wanting to sound too hippy trippy). Managing race pain, race pace, nutrition, dark pacthes etc .
For that reason i’m yet to come across any reading that would fit into what you are looking for. Though if you have any designs on big elevation races, then Training for the Uphill Athlete would be a good shout. Though you will be familiar with many of the principles discussed in the book already.
Not sure if that helps.
Happy to offer whatever insight i can offer - i’m no expert, just a guy that likes to get out and try a bit of everything - on more specific elements. Or i’m sure there are plenty on here that can be a good critical friend in terms of taking an objective look at what you’re doing and making suggestions.