IIRC Peavey usually used the same wider length J style pickups on most models so 4 / 5 / 6 / neck / bridge pickups were interchangeable except for resistance and polarity.sorry let me re phrase that
can the millenium j neck pickup he used in bridge and neck? Or is it made for only neck
This is the common rule for many J style pickup basses (nonFender style) from the mid 90's and later no matter the manufacturer. [There were some exceptions on some products like Squier or Bullet basses You will need to measure the particular bass to be certain.]