Update! This afternoon I got my coolant lines plumbed. I went into Lordco and picked random hoses that were the correct sizes and had the angles I wanted off their wall. I think I confused their parts guy, lol. I used a couple AC Delco hoses 18155L and 16136M.
I had THOUGHT the Webasto had 5/8 barbs for the coolant lines but I was wrong. They are 3/4. One of the pre-made hoses I picked has a 3/4 inch take-off that changes to 5/8 about an inch into the line, so that was perfect. The other is 3/4 all the way, then I used a 3/4 to 5/8 hose joiner where it connected to my bulk 5/8 line. I used all stainless hose clamps.
It was convenient that one section only a few inches long that I had cut off the end of one of the hoses was a perfect 45 degree and exactly the correct length for fixing the section of hose immediately before the heater core (where the 110v percolating heater was installed previously)
The end result is as close to a factory/oem look as I could manage. The formed hoses helped with that I think.
Tomorrow is electical... hooking the wiring harness up. SHORT power run to the Blue Sea fuse block (removing the Webasto inline fuse), the diesel fuel pump hookup, and running the wires inside to my centre console for the Webasto 1533 timer.
Friday morning my bits from Newline Hose and fitting will be here so I will hook up the diesel fuel line.
@dan1554 I ended up ordering a brass barb'd 1/2 inch tee with a 3/8 barbed take-off, and a brass barbed 3/8 to 1/4 hose coupler/reducer.