Your reluctance to use flame in the engine bay is understandable, but with the carb out, there isn't a big fuel source nearby. You could always drape everything around the area you want to flame with sopping wet towels. It really helps if you can get the union nut cherry red a couple of times with in-between squirts of PB Blaster or touch a candle to it. Wax is supposed to work well.
If you really are against the blue wrench, just keep hitting the nut with Blaster for a week with some taps from a hammer after: Vibrations help set up the capillary to loosen the nut.
I have a crows-foot line-wrench I use for that one. (it is 17mm, right? Been a while).
3/8 inch drive x 17 mm 6-point flare nut crowfoot wrench. Use to disconnect brake, fuel, and hydraulic lines without rounding-off fasteners. WCF16217
www.tekton.com
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