depending on how mechanically inclined you are, about 3hrs or so with hand tools, if you want to know specifics on what you need and how to do it, i can pm or email or post here. I'm use to work at a pete dealer til may 2009.

the pete i have has lot valves so draining the coolant was pretty straight forward, after that just remove alternator, the ect sensor, hose from reservoir, the radiator and another one that goes to the water pump, then you just remove the housing and personally i like to take the housing apart on a work bench but thats just me. theres some little seals that cost a few cents that would not hurt to replace the sales person at the wanted to charge me $20 to pres them for me but i did it at home and smoothly teh only thing you need is patience

Very easy job if you take your time, the best thing to do is go buy a service manual it was the best $380 i ever spent.

yes always replace the seals in the bottom where the thermostats sit into, a 2in socket and hammer works excellent, but a good flat nose punch or wood end of a hammer handle works good also, patience and some time. make sure to clean the gasket surface for the 2 halves of the housing and at the head, and should be good to go.

does the C15s run a dual thermostat? my 2000 3406E has two thermostats in the housing.

yeah its the basically the same housings not 100% but i think c15 run hotter than E's so thermostats are different