That's surprising to me, since just a few 10s of miles up the Blackstone from you in Worcester gas burner retrofits are pretty common. (There was a real run on them during the 2008 oil price spike. My next-door neighbors retrofitted their nearly-new ca. 2003 Burnham oil fired steam unit with a gas burner at that time, and had the oil tank removed, cutting their heating costs in half. It paid for itself in 2 heating seasons.)
To make a realistic assessment of what makes sense we'd need to know what the 97.5th or 99th percentile out door temp heat load is. Short of doing a lengthy heat loss analysis, if we had a zip code and your fuel use correlated to specific calendar dates, and the model/size of the oil boiler it's easy to put an accurate upper bound on the heat load. The size of the heat load, and the type/amount of radiator/baseboard you have may dictate the boiler choices. Even a single annual fuel use number and the boiler specs can get pretty close. If your oil vendor includes a "K-factor" on their billing (as many do), that helps too.
Also, do you heat your hot water with the boiler? If yes, is it with an indirect tank, or with an embedded coil inside the boiler?
Steam, or hydronic (pumped hot water)?
Radiators, or baseboard?
There may be sensible alternatives that also make more economic sense, such as putting an Intellicon economizer control on the existing boiler along with installing a high-efficiency mini-split heat pump to carry some or most of the heating load. At 15 cents/kwh electricity a mini-split would deliver ~57KBTU/$ of heat to the house, compared to an ideally-sized 85% oil boiler giving you only 39.1KBTU/$ with $3/oil, or 33.5KBTU/$ with $3.50 oil. Even if the mini-split didn't carry the whole load at +5F (which is about your 99% design condition in RI), the boiler can. But if most of the time most of the load is handled by the heat pump, your oil use would be cut by 80-90%.
An 83% mid-efficiency gas-burner would deliver 66.4KBTU/$ at $1.25/therm gas (55.3KBTU/$ @ $1.50/therm gas) but would cost somewhat more than a 2-ton mini-split, and wouldn't provide air-conditioning. A modulating condensing gas-burner might deliver 76KBTU/$ (with $1.25 gas) but would cost north of $10K up front, taking a good long while to pay off the difference on fuel savings alone.