Another way to approach this is, what's the cutter spindle rotation direction, looking from above?

If it is clockwise for both spindles, there's no reason to use left hand threads, which are quite rare on mowers.

If you can get access to an impact wrench, that's usually the most effective way to break tight fasteners loose, used carefully.

Cheers,
Gadge

"ODK Mods can explain it to you, but they can't understand it for you..."

"Crazy can be medicated, ignorance can be educated - but there is no cure for stupid..."