I ordered the Nordstrand from Bass Club Chicago. It came promptly and nicely packaged.
I was prepared for a fit issue from web discussions and comments from Nordstrand. There is no one-size-fits-all Mustang pickup, because the Mustang design evolved over the years. Sure enough, the new pickup wouldn't fit in my old pickup covers. I decided to just shave a bit off the top plate of the pickup. Don't try this at home -- the wires are extremely delicate, and one slip of the dremel would be disaster. I also tapped the holes in the bottom plate of the pickup to accept #4-40 screws rather than the original #6-32. And the mounting holes are further apart than on my original pickups.
No slam against Nordstrand here. They are open about this issue and I went in with eyes open thanks to info that they provided, but was willing to do a but of my own pickup luthierie to make this bass gig-worthy. Also, this bass is already heavily modded, so there is no collector value to worry about. This process was a whole lot easier and less invasive than installing a full size pickup.
The new pickup has a lot more output, and sounds great. The workmanship is meticulous. I think it really transforms the bass. Oddly enough I think that 30 years of playing upright has made it harder for me to play electric, and it sounds counter intuitive, but the smaller scale is just more comfortable for me now. I also no longer like the skinny thin neck of the Ibanez, and might consider an electric with an overall fatter neck next time.