Fender and motoring line size

Sorry, I can't answer that.
I crunched about 12 hundreds miles right after purchasing the boat, to bring her to my home berth, all at planing speed.
That's the reason why I know that 7 to 8 L/Nm in the 18 to 26kts range are rather accurate numbers: by checking the fuel used between fill-ups.
As you know, these engines are fully mechanical, so the only way to know the fuel burn in real time is by installing some system like the Floscan, which I don't have.
I do cruise very slowly, occasionally. But never for distances long enough to make any decent fuel calculation.
The only thing I can tell you is based on the builder's fuel consumption chart, whose accuracy proved remarkably good at any fast(ish) cruising speed.
But those charts start at 1000 rpm, with the boat making 9.5 kts (i.e., already a bit above hull speed), and burning 42 L/h, which translates into 4.4 L/Nm.
Now, based on a very long previous experience with a similarly sized displacement trawler, I would expect the fuel burn to drop further, at 8 kts or so. I guess in the 3 L/Nm ballpark, if not a bit less.
Trouble is, while I didn't mind multi-day passages at 8kts with a stabilized trawler, planing boats don't really like to go slow, so neither do I anymore.
It's the nature of the beast, so to speak...