The two fluid levels will equalize through the hose & fittings. Which makes me wonder what happens in a long, steep climb or descent.
Using the anodized aluminum fittings always drives up the price. If you go with steel & brass fittings the price can be considerably lower.
The Weatherhead p/n for the -8 X M18x1.5 steel adapter fitting is MC5315x8x18
According to
here they are $3.36 each
The hose ends are known in Weatherhead-speak as "Series 100 'B' Barb-tite" hose ends. A straight hose end's p/n is 10008B-608 My book does not show the 90* hose end, which is odd. Called my local vendor (Ventura area of SoCA) and asked them for a p/n. A different mfg, but: JF90-8-8 @ ~$13 each (PM if you want that vendor's name & contact)
The blue hose that I use at work on these fittings is Aeroquip's FC332 hose. I've immersed this stuff in gasoline and in diesel for over a week with no trouble. Normally a hose will carry such fluids thru the center just fine, but doesn't like having it around the outside. I've had it laying against hot turbocharger parts during testing and it barely chars and is still completely serviceable.
BAT sells it for $3.39/foot
Looks like I could build this for about $42 sourced locally.