I have another Precision that I made into a PJ (with the J pickup in the 70s position and Tony Franklin wiring) and it's great. The Wattplower wiring is interesting, but it doesn't give you any 2-pickup sounds and that is primarily what I am looking for in adding the 2nd pickup in this case.
My other thought was that, with a PJ bass, you have a somewhat weird signal blend because the distance between the low strings and the J pickup and the high strings and the J pickup is different. Using 2 split Ps oriented in the same direction (both reverse or both regular) eliminates this whereas having opposite orientations would make it even more extreme. Since I already have a PJ, I figure I'll keep both pickups the same orientation for a different effect when both are on. As a bonus, it looks better to me too!
There is the question of whether to have the pickups reverse or not, but based on sound samples I've hear and my own experience with the current split P in the regular orientation, I think I'll be fine with both of them int he normal orientation.