Helical cut = quiet + end thrust
Straight cut = Noise + no end thrust

Chains impart no end thrust & straight cut gears replicate this condition but make noise which is magnified by the idler gear as there are now two places where this noise is now generated.

Engines that were designed with gear drives in the first place make provision for end thrust, they use quieter, helical cut gears, & they use a steel crank gear & cam gear of a softer material [resin/ fiber was common] & they used two gears only.
This resulted in a positive drive, no noise, reliable operation & reasonable cost due to the reduction in the number of parts needed.

This aftermarket set for Datsun A series would be really good on a competition engine, if only it was affordable.