5 String MusicMan® style pickups come in 3 different shapes, and it is worth the effort to take a quick measurement as you dive into the pickup selection process. Not all pickup manufacturers are making pickups to fit all of the different shapes. When taking a look at the different sizings and comparing against your bass's pickup(s), a couple hundredths of an inch (.01-.03") difference, should not present an installation problem.
Here is a breakdown of the different shapes:
• Short ~3.5” (88mm) x 1.9” (48mm) - This size is the same as a 4 string MM pickup, measurements not including the screw ears.
• Ernie Ball® Stingray® ~4.38” (111mm) x 1.92” (49mm) - This model is most like a large soapbar shape, and does not have screw ears.
• Lakland® ~4.14” (105mm) x 1.91” (49mm) - The largest of the shapes, looks like a long 4 string MM pickup. Measurements do not include the screw ears.