Speedway Motors has Joe Gibbs Driven Oil on sale right now. Hard to beat this quality oil for your 340 engine. HR-2: 10W-30, or HR-5: 10W-40.

https://www.speedwaymotors.com/Driven-Racing-Oil-02007-HR2-Conventional-10W30-Motor-Oil-12-Quarts,272680.html

http://www.drivenracingoil.com/