Bob Shade tells us this:
Hi Chris and welcome to the forum!
This is from the first Japanese run of Mosrites from the 70's.
This is rare, you see the 6 string models infrequently but rarely ever a bass. I have no idea how many of each were produced, but this may be the first bass I have noticed from this period. The 6 strings I have seen around since conception.
The 6 strings trade for about $800.00 to $1300.00 depending on condition. Some guys and even dealers don't know that these are early Japanese models and have been advertised at vintage USA prices.
Study these and be sure if you are looking for a real USA Mosrite that you are getting the right guitar.
Bob