A quick question from an HVAC novice...

I have a roughly 210 year old house in new england with two completely separate oil heat systems (about 2/3 of the heat zones and hot water run off one and 1/3 of the zones off the other). two separate tanks feed them and they are in different basement rooms and vent through different chimneys. i'd guess the boilers are 20+ yrs old or so but my oil company service guy says they are in "good shape". my question is... does it make sense to convert one of the systems to gas (i have a gas line into the house already) since the modern gas boilers may be more efficient and at least lately the cost of gas vs oil has been much lower. can i link my two oil tanks to increase my storage capacity for the remaining oil system if i do it? thanks for any input.