40K load even @ 0f for an 1140' house would be on the very-high side of a house that had insulation in the walls, and glass in the windows. Most would be about 30K @ 0F before improvements.
Don't count on the pros for precision on the heat load, unless they give you a printed out Manual-J and all of the details of the inputs check out. Most online heat load calculators have drastically high air infiltration default numbers too.
If you have a "K-factor" stamped on a mid to late winter oil fill-up, or some oil bills with exact dates & amounts we could narrow in on that by quite a bit. A ZIP code can help find the nearest weatherstation for more precise weather data. It can be even further refined by knowing the thermostat settings (including overnight set-backs, if any.)
How many feet of convector per zone, and how deep / tall are the fins on those convectors, and how tall are the cabinets?
At typical 26" tall convector with 4" square fins is good for ~1500 BTU/hr per foot @ 190F AWT (200 F output on the boiler, 180F back), or about 1250 BTU/hr per foot @ 170F AWT (180F out, 160F back.) With 64' total and a 58K-out boiler you're looking at ~900 BTU/hr per foot, which balances at about 150F AWT, which is fine- the boiler would run a continuous burn during a call for heat without running into destructive condensing temps. But...
With only one zone calling for heat, even it's split 32'-32', that's 1800 BTU/foot. The boiler can't run hot enough for only 32' of convector to dump that 58K of heat into the zone, so the boiler will cycle on/off during calls for heat. It probably won't short-cycle itself into super-low efficiency, but you'll lose some, and it's less than ideal, and to keep cycle counts down & efficiency up, a heat-purging boiler control would be a good idea.
If your heat load is as low as it likely is, there are smaller boilers that would run more efficiently and effectively without cycling on single-zone calls.
Without more info on the actual convector size (and amount of convector on the smallest zone), or the and fuel use it's hard to pick a boiler. A 58K boiler would be fine running that radiation as a single zone, but it's almost certainly oversized for any one zone, and 3x oversized for the the whole-house load level you'll likely be hitting if you get serious about upgrading the insulation & air sealing. You'll probably be able to get the place to 20K @ 0F without breaking the bank if you're judicious about it.
If you're going to go with a 3-plate/60K-ish boilers, the 3-plate Burnhams come with smart controls and are tolerant of low return water temps and wouldn't short cycle. But there are probably smaller/better choices out there for both your current and future loads.