1 5/8 = 1 10/16. So, the overall difference in width between the two necks you're talking about is only 1/16", or .062, or the width of a heavy low E string. Spread that over 6 strings, and you're only talking a change in string spacing of about .010, or the width of a high E string. In other words, it's not that much. You wouldn't be able to see it by eye. I wouldn't sweat it, but people make decisions based on less than that.