I figured you did know. It was just almost like a little mental check-off box where I needed to see a check.
I had been told the gentle hit-hard hit method of worming by my livestock vets. I myself had seen cases where horses were wormed and had either the shock or enormous numbers of worms trying to pass. I had heard of at least a couple of cases of blockage. There was one case of chocking in a poster's bird where it was directly after worming for a case of heavy crop worms - and I do wish I could have been able to cross through my computer and do a necropsy to see if it was worms. I'll never know, I suppose.
The worming was firmed up for me after I had a very experienced poultry owner tell me the same - and I remembered it from vet recommendations. It just makes sense. And really it's just a one-time thing.
Oh and worms - don't worry, I do the same. Honestly my last worming was quite overdue for the same reason. "Well they look good - and I'm experienced enough to know when they look good...." It was a bird with lice that made me get off my tush and finally do this "spring's" worming. Mid year.
On the ivermectin pour on, I use 1 drop for a small OE hen sized bantam, 2 drops for an OE male to a regular small bantam, 3 drops for an average bantam or very small commercial hen, 4 drops for an average adult chicken or small large-breed hen, 5 drops for a large large-fowl bird, and 6 drops for giant breeds, a large bird. That's the blue "ivermectin" not any other '-ectin'.
I use a 3 cc syringe with a 25g needle. I of course don't inject, but I find the needle makes a very precise size of drop and allows me to place it better. I hold the syringe horizontally in case the chicken hops up so I don't poke it. Then you just have to find a very naked spot on their skin - between their shoulders or at the back of their neck works best for me. If you get it on any fluff, it will absorb into the fluff at lightening speed and then you don't know if they get it or not. So aim for very bald skin on their main body.
I treat withdrawals just as indicated for cattle. Ivermectin is not at all labeled for chickens, so we don't really know. However since it is used to treat worm infestations in humans - I like to assume that the amounts in eggs are probably safe for humans if not pregnant. However, I don't like the thought of worms being shed into an egg - so I personally withdraw for 2 weeks "just because it's icky" - such a scientific reason.
Levamisole is also a good choice if you choose it. I simply like ivermectin because it's quick, easy, safe, gets externals - that's the kicker for me.
And I'm honored to be able to help. When I needed help, often it was not there. (And when it was, I was so grateful for it that I wanted to be just as helpful as the generous people who helped me!) So it's truly my pleasure. I learn something every day, and intend to keep that going until my last day on earth. And why learn stuff if you can't share it, right?
I'm glad this helped. Please let me know which method you choose, and how you like it.