( Fenbendazole) Safeguard Paste or Liquid is the same dose.
For treatment of Roundworms Only - dose is 0.23ml per pound of weight given orally once then repeat in 10 days.
For treatment of other worms including Roundworms, but not Tapeworms - dose is 0.23ml per pound of weight given orally once a day for 5 days in a row.
You may not need to weigh every single bird, but knowing the weight of some of them would be a good idea so you can give the most accurate dose possible.
Nothing says you have to worm ALL birds at once. If you have a large number of birds, then split them into groups. Say you do all the bantams one week, then maybe all of another breed another week, etc. Break the numbers down where it's manageable.
I've found it easiest to have syringes pre-loaded with de-wormer, then go out early while birds are still roosting. Take a bird off the roost, give her the meds, then set her in the floor. Takes just a few minutes if you think it all out and are prepared beforehand.