What size Nicson? the 1" will pump a ton of water. I swaped a few years ago from the neovane to magnaflow because I was constantly fighting temp increase while ideling, I hvad the pump on the motor from 95' to 2009 and have friends that run the same punp with no issues. I had good impellars no obstructions, I just had one head that would always run hot. Swapped to the magnaflow and no issue at all. I went with a 1" and it was too much water though having a hard time getting heat in it now. I do take the impellars out and put them in a zip lock baggie when I put the boat away and just changed my first impellar last summer, made the swap in 2009.
For a Bravo application I would use the Mercruiser style belt driven pump. It uses 1 1/4" inlet and outlet designed with high suction for pulling water through the drive, and low pressure/high volume. The stock water fitting on the transom assy is 1 1/4".
There are a few mfg's that make that pump for less that the cost of a Mercury pump