A 1965 Chevy didn't come with a 350 and HEI. Best guess would be to use a spark plug for a vehicle that came with that engine and ignition. If the engine has iron heads, it probably needs a tapered seat plug. A good starting point would be R44TS or R44T(with washer) if not a tapered seat plug. For plug gap, try about .045".
.35 of an inch
.060
.045.
It is .060...
.060
Correct gap is .60
gap is .060
According to Champion spark plug applications chart, the correct gap for 1995 Chevy Tahoe 350 engine is .035
.060
0.035
The 1989 Chevrolet 350 cubic inch engine spark plug gap is dependent upon the engine application. The most common spark plug gap for the Chevy 350 engine is .027.
only use AC Delco plugs, there the only one with the correct heat range.