I need to use a step bit with a 1/2" shank. I only have drills with 3/8" chucks. Is the arbor size on most drills a standard which would enable me to just replace one of the 3/8" chucks with a 1/2" chuck? Is it really that simple?
You're looking for Jacobs part number 31037, it's a keyless 1/2" chuck for standard 3/8" drills designed specifically for the purpose of converting them. Your 3/8 drill will be fine with a 1/2" chuck, I've got a few than have been converted, 2 air powered, 1 corded/electric and 2 cordless. Just treat the drill as you normally would, drilling holes larger than 3/8" with a 3/8" drill has never been a problem.
I converted my first cordless drill for the same reason, needed to use an Irwin Unibit with the large shank.
Ok, I've done some research and it looks like a 1/2" chuck can be used on a 3/8" drill if the chuck is threaded 3/8"x24M. I was able to find a Jacobs MultiCraft (#30598) that should fit my mid-90s Makita.