Given the 80% attrition rate of BUD/S, you need to stack all of the cards in your favor before going out for SEAL training. BUD/S is *not* designed to get you in shape, and so you need to take this task to hand before enlisting (or before putting in your packet for BUD/S, if you're already in service).
Also keep in mind that the PST minimums are just that – minimums. If you can only score a 42 on the push-ups or 6 pull-ups, you're going to have a very high likelihood of becoming a DOR. And if your heart's in the right place, you're still incredibly likely to get dropped after you hurt yourself because you're not in the physical condition necessary to train successfully at BUD/S.