VP TMD41 thermostat question

[snowbird30ds]

I posted this on the mobo forum but thought it may do better here under the "practical" banner.
One of my engines doesn't get up to temperature at river speeds so I'm guessing new stats would be in order, what other o'rings and gaskets are needed? What comes with thermostat kit 3831424?
Engine is a TMD41A volvo penta.
Possibly a question for @volvopaul
TIA.

 

[snowbird30ds]

As a follow up to this I just got a delivery of seals and pattern thermostats from keyparts, under the keypart label on the stats is the motorad part number, 233-82JK if anyone needs one, much cheaper without a VP number on....