Hello ted, below is a link to EFMheating's website and a copy of the owners/instalation manual for your DF520.
It sounds like your house has most of the plumbing done. You probably will be able to just put the EFM in the same location as the handfeed boiler, or where the propane boiler is. The plumbing hookup should be pretty simple.
Make sure your chimney is in good shape and clean if you have been burning wood. The EFM stoker boiler requires a good draft to function properly and keep fumes and smells out of the house.
If you can separate the supply and returns you will like having separate zones for each floor. A separate zone for a bathroom is a real luxury.
Once you get your stoker boiler hooked up, you won't believe how nice it is to be free of the chore every 10-12 hours of feeding the boiler. With an EFM 520 in a 1200 sqft house, you should only need to empty the ash pan every few days to a week. Keep the coal supply [coal bin] dry, you don't want wet fines clogging the feed to the auger.
Check out the forum for EFM boiler photos and already asked questions. I think you will find a lot of information.