your starting a new style. the answer to your question is: Practice, practice, practice. the BB style puts more stress on the pecs to move the weight off the chest, then the front delts work crazy hard throughout the next roughly 8"with some help from the triceps, finally the triceps take over and do most of the work to lockout.
With the powerlifter style of elbows tucked you get more muscles helping to move the weight off the chest: Pecs, front delts,traps, lats and tri's. More muscles helping the front delts during those first 8":lats, traps, tri's. which if you train for the speed and explosion off the chest should give you momentum through the lockout thus helping the tri's to do so.
practice, practice, practice.
Find a real powerlifter IN your gym, or find out where some REAL powerlifters train and go join their gym. There is only so much ANYone can do for you over the internet. Any real tweaking to your form MUST be done in person. Video's don't provide enough information and neither does the typed word.
