I thought the mantra was " if you spin with a posi, put an open in it; if you spin with an open rear, put a posi in it." With spin sensitive cars- like high power, short wheel base- with a posi you light up both rears thus losing mechanical grip and are more likely to go around while an open rear which is putting power to both while having traction, only one spins when you exceed that so may still have some directional stability. At least that's how I interpret it. Have had posi in all my cars without issue ( except once when I had a set up where the center of gravity was moved way up and the car was squirrely from the start and on one run I got distracted and lost it, spinning. Fixed the CG issue and now goes straight again. Course I don't have the power to spin the tires at any speed like some so maybe my experience here isn't worth much. I don't think you have any issue with a welded rear, MM. Causes more trouble pushing it around in the pits or on pavement though....