Welcome.First before anything,what size house,original boiler size,insulation,how drafty,and possible heat loss calculations.You need to know what size boiler is needed first.I'd go with a stoker boiler and keep the harmon for electric outages.
I'd tear out the old boiler and replace it with a multi fuel stoker boiler(coal with oil back up)
Most likely you old boiler has ASBESTOS wraped around it, if it's the size of a VW.Big money for asbostos removal,but you can remove it yourself.Just water the boiler down with water so no absotos is disturbed and flying around,then put in trash bags and toss in regular garbage(do you really thing the pros dispose the "toxic waste" in a special place,it go's to the same landfill as your trash) and save $5000.00 and buy your coal boiler with the savings.
Depending on boiler size needed:
EFM 520 with oil back up
LL 110 with oil back up
The oil back up is not as effecient,but it's a back up and not going to be used except for when you go on vacation or unexpected long term trips.