With a cross over system, to increase water temps you want to restrict water after the engine - ie: at t-stat housing - with restrictors (those big washers with holes) or a t-stat itself.
These may create more water psi than you want - therefore you have to check this. If you find the correct restrictor and it causes more psi than you want, then you need to run a psi regulator just before the restrictor or block that will dump the excess water over the transom.
Some people successfully use threaded brass plumbing water psi regulators and many pony up and buy the cheap but of course expensive Mercury Racing water psi valve.
I would start the cheap and easy way. Get a Moroso or other water restrictor kit. they are cheap and come with a handful of restrictors that vary in orifice size and fit where a t-stat would on intake manifold. Watch your temps and watch your water psi. If both are where you want with no more mods needed, then your all set. If either or both aren't where you want than it's time to run a t-stat with bypass and water psi valve.
Thank you once again Cfm. I will be trying the restrictor kit once I get the pressure gauge installed.