So if I'm converting to through transom, direct sea water pick up in lieu of the lower unit, where do I put a pressure release valve and where or how do I dump the overflow? Thx . P

WOW.. No one has any input on this???

Between the sea strainer and the raw water pump. You'll need a new through hull fitting for the dump hose. Keep in mind that Mercury lists maximum pressure at 43 psi. I run near that at WOT and often higher. I know someone who regularly runs 60 psi. If you install a 25 psi dump then the engine will not get enough cooling water. I put one on mine that was set at 35 psi. On the advice from Brownie, yes, Brownie, I removed it. I reconfigured the water inlet on my Imco shorty to get pressure where I like it and can lower the pressure by trimming up. You should be able to adjust your new water pick-up to get pressure where it should be.

I'm thinking setting the release pressure at 45, but where do I dump it? Can I just dump it to the exhaust tips? and where do I put the release valve?
I take Brownie's advice anytime.

I put in a new through-hull next to the bilge pump dump.