Have to agree with Dave, if you have a Ford 9" you cannot go wrong, street use, go for a good 4 spider possi. If you have 31 spline axels all the better, because with those big tyres on one end a big HP motor on the other end sometning has to give. So your 31 spline axel will give you more insurance over a 28 spline. On the strip or burnouts, have another center section with a mini spool, so yo dont have to much money tied up in a detroit locker. And you wont have to rebuild the clutch pacs to often in the posi.