Ultimately, it's your call.
If you can get the lip on the step to seat down well so that it hooks on the tramp side of the crossbar AND you get the rivets pulled tight (rent / buy / borrow a heavy duty rivet gun), I don't think you'll have any problem with the enlarged hole in the crossbar.
In any event, it won't go catastrophically - the rivets will stretch, the lip will start to lift - you'll have lots of warning that there's a problem. (I'm talking over the course of several hard sessions of sailing). It's only going to move an 1/8" until it hits the front of the hole anyway.
The advantage to putting the step in the "new" location is that you'll be able to rake the mast back further, which will give you better upwind performance and controllability.
Thanks for the compliment. I've been racing 16's for over 30 years now - I'd like to think I've seen / heard / done almost anything with them & I'm happy to share. Occasionally I do get down to a regatta in your neck of the woods - I grew up in Richmond and raced up and down the east coast when I was in high school / college. I still have a number of Hobie friends from that area. You should hook up with Hobie Fleet 191 in Greesnboro. Their web page is here