I have installed a few, including on the Yanmar, JD 770.
No biggie. Wouldn't give the dealer money for doing this, especially since it means getting the machine to them.
I have found very little internal room for some of these heaters. You turn them only slightly and they no longer fit properly in the hole, so you twist them back and forth to find the right spot.
Come to think of it, I did have a problem with one. I had to modify the tightening bolt, because there wasn't enough travel on the threads to get the thing tight. You would tighten it up til the end of the threads and it would still be loose. Remember saying a few choice words!
How handy are you anyway? lol
You need to drain off some coolant, of course, saving it for reuse. Don't do it HOT!
Put some grease on the bolt threads to make things go a little easier as well.
Oh, as for your question of source, not sure. Depends on price difference. Spending a few extra dollars to (hopefully) get the right one, may be worth it to avoid any hassle, especially if you saved the labour.
Edit: Make sure you tie wrap the cord, where it will be handy, but away from the exhaust manifold and that nasty spinny thing!