I just put a crossover on my 454 and was curious as to where I can relocate the water temperature to? There was also one other small wire on the thermostat housing when I removed it. Second thing, my boat doesn't have an oil temp gauge on it. I saw somewhere where Eddie Young suggested putting it on the port side above the oil filter block off plate where the oil pressure sender is, but where would you relocate that sensor? Is it even worth having water temp or should I just get rid of it and monitor oil temps instead?

Deffinately don't want to get rid of your water temp gauge. Sender should be on the front of the intake manifold in the cross over section of the manifold near the thermostate housing. Should have a Tan wire.

Where was yours at?

Personally, I think you should have just left your stock engines as stock.
Crossovers can create all kinds of issues and will have no benefit on stock 454's.
You now need to monitor water temps, water pressure and oil temps to make sure all are within acceptable ranges.
One of the senders on the old T Stat housing was for the gauge sender. The other sender with other wire(tan/blue) was for the high water temp alarm.

Griff I contemplated this issue a lot but I really wanted to just clean up the motor area and remove some moving parts. I have read 100's of threads over the years it seems like and it's all probably stuff I should be monitoring regardless.

All of mine was in the thermostat housing which is now gone. So I'm guessing there is some kind of plug I can remove on the intake manifold. The reason I really decided to replace it all was when I removed the tstat housing it was horribly corroded. I looked at just replacing it and decided to just kill to problems at he same time.

There should have been two senders, two wires, going to tstat housing. One for water temp (tan), and one for water temp alarm switch (tan with blue stripe)

In your harness, there may be a brown with white stripe wire. Sometimes they may be taped up and unused. If you have this wire, that would be your oil temp wire. You'd need to add a sender for it, and obviously the gauge.

For sender placement, you should have a plug or two in the front of the intakes, next to the tstat opening. Or, one underneath the tstat hole in front. Any of those will work for water senders. For oil temp, depending on where your oil psi sender is mounted, you may have a 1/8th NPT plug in the filter adapter avail to use. If not, I would mount the oil psi sender along the pan rail on the port side of block. Several 1/8th plugs there you can use. Then mount the temp sender at the filter.

I'm with Griff on the Crossovers can create all kinds of issues.
I run them only because the first set of engines came with them. I have also purchased all the parts to put water pumps back on.
If you run Crossovers the gain in HP is so small you will never see it. Most likely you will run into water pressure problems.
I run pressure relief valves and have water pressure gauges
to monitor it. Also the heat of the engine can fulucate up down up down.
IMO - I would only run them on a blown application.

I've been running a crossover for several years now with a thermostat and my engine temps are solid unless it's extremely cold. I put the boat in Northern Lake Huron when the water temp was 35 degrees, engine never got over 135. Other than that, the only time I see the temp rise is when I drop to an idle after a long hard run, engine will climb to 190 from 160 than drop down in less than a minute. My intake has a port on either side of the thermostat housing that I use for the 2 sending units. as far as the oil temp, I have a remote filter that I mount the oil temp sender in. I run the oil through the remote filter than the cooler.

As mentioned above I am really not looking for HP gains or increase. I am looking for a cleaner bilge and less moving parts. Adding a oil temp gauge and an water pressure guage is not that big of a deal if it cleans up the overall look of the bilge.

You should have two plugs on the remote oil filter where you can put your oil temp sender. Remove one of the plugs, install the sender.

Correction- looks like you only have one plug. Put it here. Looking at your plumbing your oil filter should be before your oil cooler so you would essentially be getting pan temps at this location.