I will be doing the same with my IR thermometer. I am going to change out the OEM manifold/risers to IMCO (have two sets) this fall unless I have a problem before that. I will also check every hose and fitting I can, along with a new impeller to make sure there are no other obstructions. Water flow out of the exhaust appears to be pretty good. Port may be spitting a bit more water than SB, but it looks pretty much the same. 15*-20* diff in port and SB at 1500-1800 rpm in water isn't that bad and apparently pretty normal.
If it gets worse I will deal with it then.

A short update... After tearing the front end of my motor apart this week, I finally decided to open up the oil cooler and check it for debris. I actually expected to find some small rocks there, but instead I found one complete vein of an impeller laying flat across the inlet blocking probably 60-70% of the water flow. Clear other than that. Thinking this may have been the root cause of the steam and overheating problem I was having. Will see, once I fire it up next month.

Curious if the current impeller is shredded or did the last person to change the impeller not backflush the system to make sure there were no problems in the hoses. Will find out shortly, when I replace the OEM sea pump with a Hardin Marine SS sea pump.

Check thee hoses for more pieces

Checked the hoses and it's all clear. Fired it up today for the first time with the new manifolds and risers. Ran it on the trailer at the ramp. Temp was 20* higher in the starboard riser. Did not get over 114* after running for about 45 minutes. Still 20* temp separation. Much better after clearing the oil cooler inlet.