3.09 4 Speed Gear Set Strength

Can I use the slant 6 / 318 gear set with the 3.09 1st gear behind my built 340 stroker motor?
I want the low 1st gear to offset a 3.23 rear axle ratio. Tranny guy was questioning if the gears were as strong as the 2.66 or 2.47 gear sets. Will they hold up?
This discussion ventured off onto overdrives, but your question was about the non-overdrive '64-5 and mid-'70's trans with 3.09, 1.92, 1.40, 1 gearset, right?