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Much thanks, Zac.
Also, FYI, I came across an H70 engine manual circa 1980 which lists Champion J8 or J17LM as the recommended spark plugs (non-resistor):http://www.brentchalmers.com/Manuals/SuperTomahawk5-8-2GC_OwnersManual_TecumsehEngine.pdf
I started another thread about this manual, and someone said they might have one circa 1970. I'll let you know if it pans out.