Perkins 4.108M temperature sender/gauge problem

[Ruso]

Gentlemen,
Own the boat for short time.
Temp gouge with moderate engine load shows 225F - no way. Confirmed with temperature gun - 180F. Thermostat original Perkins was placed by me and temperature reading shows it opens properly.
Now, before ordering a new temp sender did some measurements.
The boat has two instrument panels in pilothouse and cockpit.
Cold engine temp is 60F(18C)
Temp sender connected - gouge in pilot house shows 72C - in cockpit 79C
Temp sender disconnected - gouge in pilot house shows 60C - in cockpit 70C
It seems they consistent to some degree - shown temp drop 8-10C
The sender resistance 400 Ohm - Ouch... It seems should be 240 Ohm and dropping when the sender warms. No?
Checked sender wires going into contact panel which splits into two (one for pilothouse - another to cockpit - no issues. Cleaned the sender contacts - no effect.
Questions:
Both gauges shows temp (see above) when the sender disconnected. Normal??
Parts4Engine says "This will not fit directly into to a Perkins 4.108 cylinder head unless you have a reducing adapter. " See picture attached. Is there adapter?
May be someone can point where I can get the sender in USA (with part number)
And thank you for reading the entire post.
May be you can advise something else?
Many thanks!

[a64pilot]

It appears you have an adapter already. Depends on if you want to take a chance and the availability of an adapter.
I would order an adapter anyway as it’s likely less than $10.

Sometimes a sending unit is actually two individual sending units in one piece. as you have two electrical connections that’s possible, if so be sure you order a sending unit that has two spade connectors.

[Ruso]

They called two-wire "isolated earth" I guess. Green and black wires. I don't have high temp alarm - at least on the panel.

[Ruso]

Now it gets really interesting. It seems the sender designed to work with 2 gauges it explains 400 Ohm resistance on it.
When I keep both instrument panels ON - both gauges display temp dropping by 30F. On 70F engine temp it shows 100F - which is still high but considering it is lowest temp range the sender/gauge designed it might work out when the temp close to the middle of gauge range 180F/200F. I will run the engine tomorrow with temp gun measuring temp on the sender.