It depends on what heads and ignition system you're using.
You'll have better luck with AC plugs in a Chevy.
Champion J8C
what is the champion cross reference for a briggs and stratton spark plug 691043
Champion RN4C - Gap .030"
Use a Champion RJ19LM set to a 0.030" gap.
An Autolite 258 is the recommended spark plug for a 6. 5 horsepower Tecumseh engine. A Champion RJ19LM also is recommended by the manufacturer.
Other spark plug brands which cross-reference/interchange with the Champion QC12YC include: NGK: BCPR5ES Denso: Q16PR-U As for what applications the spark plug fits, it fits various European applications, such as BMW, Mercedes, and Saab.
Champion F-14Y, gap .034".
Champion RC-12YC at 0.030"
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With a few bucks, anything you want to put in fits.
Champion RC12YC or E3 Diamond Fire E3.20
Autolite 258