I agree, our 23-172 looks like a dead ringer for your old guide; so much so, in fact, that I ran in the back to remeasure it with my own pair of calipers. Wouldn't you know it but our dimensions are just about the same as yours.
I say "just about" because the base appears to be an uneven hex shape. My exact measurements were .427" at the absolute skinniest and .490" at the absolute fattest. You might want to triple check yours just to see if it aligns.
The dimensions you see on our store page were given to us by the manufacturer directly. I don't know why they labelled this an even 3/8" but if I had to guess then I would say that this is the size of the hole it fits into. Or they just thought it was easier to round up. A LOT of manufacturers label their dimensions that way. Either way, I feel confident that our 23-172 is exactly what you want.
You got it! Please let me know if you ever need anything else.
