X2 what
@Jefferson10940 said. Take your time and if you need to know the size Buy a set of bits and just slide one in that is the size of the hole.
When drilling go slow and start small then work up to the actual bit size needed. I will also say that if you can get a punch to make a small dent/hole basically just to mark the drill spot that will prove beneficial as it puts a small groove which will eliminate the drill bit rolling or sliding out of the intended spot.
Did the mod this weekend and it went fairly well. ^^^^This was the key advice here which I didn't see until this morning.
Another bit of prudent advice would be to practice drilling the holes on the piece of I-beam you are going to cut off/discard. I didn't do that, so I messed up my first hole by fractions of an inch and the step doesn't quite sit flush. I think there is still plenty of material to hold the bolt, but I am going to use that as my bottom step just in case. After screwing up once I figured to start with a very small bit and work up and was golden.
Also climbed a tree out back using the movable aider inspired by DaveT, wow what a smart way to use an aider. I haven't experienced any issues with deer seeing aiders, for me the huge benefit is how much it improves the packability. I kept my 2 step aider on the bottom stick for now and got to 19 feet using the movable aider on the other two.
Finally one last very very minor thing I did which I don't think I've seen mentioned with the heliums, the top of the I beam I just took a file to it and rounded the edges off. Mine were surprisingly sharp out of the box and prone to snag on things.