Very difficult to estimate without clearer pics of the body (front and back), and neck. The J pickup could have been installed professionally or it could have been installed using a screwdriver to carve out the opening. Regardless, the originality is no longer there so the value as a collectible is gone. The bridge cover is probably not available as well as the case.
If the bass is in good playing condition and the truss rod works it might be worth $500 tops if a Ventures Model is a priority. Otherwise I'd lowball it at $300. You can find early 70's 2-pickup models (non-Ventures) for less than $1,000 usually. They tend to have cracks in the clearcoat but this one isn't a showpiece either.
Layin' it down since 1964. Mosrite Owners Club #2. Vintage Bass Club #9.