I have a 2006 Highway One P-Bass. I used to have an 07 MIA P-Bass, and the two stock/factory pickguards on the 2 basses were the same. All the holes lined up and all.
I tried the different aftermarket pickguards that I got for one bass on the other bass, and they were absolutely fine fit-wise. I got the pickguards from All-Parts, Stew-Mac, and WD Music.
And the pickguards all fit on my Squier VM too.
YMMV
Here's a shot of the Stew-Mac tort pg on my HO.
