Welcome to BC
Second pickup is not original and will have a detrimental affect on the price now. By how much, depends on the buyer. If there are lots about unmolested and in better condiiton then it will be worth much less. As you are in the USA, there will be more around than over here. Decent ones seem to be around $5000 upwards, I would not like to say what yours is worth.
I bought a 72 Telecaster Bass which had a similar modification i.e an extra pickup. I've since returned it to stock but know its value as 100% original is affected.