I am pretty sure yoyos would be fine in that tank for a while IME as the ones that I have had in my 72G for 6 months are still 4" and I got them at 3.5". Assassins work, but you hardly see them, if you have a mag float, just smash up all the snails that are on the sides/front/back of the tank.
I found that slices of cucmber was more effective than lettuce for drawing the snails. Be sure the snails are dead before discarding by freezing them so they don't infest anything else.