So many people weighed in on this project that I thought I'd post an update, even though it's been a while.
We ended up having a
Baxi Luna (HT) high efficiency propane boiler installed. Jay Brittain did the work, as he provided the best estimate and I trusted him (He had done some smaller jobs for me in the past). I had four (4) estimates range from a high of $18,000 to just under 10K, which is about what I paid Jay for the conversion.
Interestingly, everyone had their pet product to push. Jeff Seymore, who was recommended by Broadhopper (I think), would only install
Munchkins, another guy swore by
Buderus, and almost everyone had something bad to say about everyone else's preferred boiler.
Fred Fuller ended up being our propane supplier (best price; plus they were our oil people and we never had any problems with them), and I paid a private party to dig my fairly complicated trench. It's now been almost one year since the conversion, and everything is going well. Besides the new boiler, which is working great, we now have a propane cooking stove, plus two propane fireplaces (very nice when the power is out).
So far, I'm not sure how much money I'm saving, if any (given the additional demands on fuel), but it sure is nice to have those two large oil tanks gone from our basement! And the Baxi, which is much more compact and hangs on the wall, takes up less space than the old oil furnace and is much quieter (not that that was really a problem).
Gathering all the info on this project, and getting all the pieces to fit, took quite a bit of time. The biggest hurdle ended up being getting that trench dug! The big companies thought it was too small, the small ones didn't think they had the equipment, it was not a simple straight-line trench and everyone had a different opinion about "requirements" (depth, etc.). But once that trench was dug everything else fell neatly into place.
Thanks to everyone who provided insight and tried to help me out. All information was greatly appreciated!