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I havn't done it yet, but you can keep your injectors. If you get bigger injectors, you'll most likely need an even bigger HPOP. I know with just a chip, and stock injectors, I'm always out running my stock pump! I believe most of the performance to be had will be at high RPM's, especially under load.
Just for a "heads up", if you do the change and your original IPR is working fine, put it into the "new" pump. My son did the switch and the IPR died a couple miles down the road. Towed it back to the shop, replaced the IPR with the original and it's good to go. Runs fine but he had put in single shot injectors and the PCM from a newer year.