All hydronic boilers (including steam boilers) can be set up to run fine with an indirect, with controls to run the indirect as a separate heating zone. Most high-efficiency modulating-condensing gas/propane fired boilers have a built-in presumption that there is going to be an indirect, which may require higher output temps than the other zone-calls when operating under "outdoor reset" control (where it raises & lowers the output temp of the boiler in response to the outside air temperature.) But even simple minded cast-iron boilers work fine with an indirect. If yours is a smaller boiler (and almost all should be relatively small, in a house that is insulated and not gargantuan in size) it's better to control the indirect as a "priority zone" , which inhibits the space heating zones from drawing heat when the indirect is calling for heat, which results in much faster recovery times on the hot water tank.
Any time you're buying a new boiler is the golden opportunity to "right size" the boiler for the space-heating load. Almost every boiler installed in 1966 was at least 2x more than was needed, and if the house has been tightened up and insulated, windows upgraded, etc. it's almost certainly going to be 3x oversized. There is a cost in operating efficiency when oversizing a boiler (even a modulating boiler), not just the up-front cost. Before you drop serious coin into a boiler swap, insist on a "Manual-J" type heat loss calculation, based on the 97.5th or 99th percentile outside design temperature, and no lower. If the HVAC guy doesn't know what you're talking about, find somebody who does. An example of what is NOT a heat loss calculation (but still common amongst installers) goes something like "Lessee, ya gots a 2400' house, times 30BTU/ft comes to 70,000BTU/hour." This type of calculation reliably oversizes the boiler by 2x or more, costing you more up-front, and every heating season thereafter in reduced efficiency.
If yours is oil fired boiler there is a lower limit to the BTU output that oil-burners can run, and that may still be 2x oversized for the heat load. If that's the case there are good/better/best options there, but I won't elaborate without more info.
If yours is a steam boiler, the boiler has to be sized for the size of the baseboard to function properly.
If it's pumped hot water (likely) the amount of radiator or baseboard is not a factor in the boiler sizing, but it may factor into how the near-boiler plumbing is done. Don't let somebody talk you into something along the lines of "Lessee, ya got 125 feet of baseboard, times 600 BTU/ft comes to 75,000BTU/hr, that's the boiler you need." which is easily as-bad as the BTU/ft methods. If in fact you have 125feet of baseboard and the Manual-J type heat load calc says your heat load is 35,000, it means you can run the system at 140F instead of 180F and keep up even on the coldest day of the year, and get better efficiency out of even a tiny 2-plate cast iron beastie, but it also means that most of the time you could run it cooler than that, and get SUPERB efficiency out of a modulating condensing boiler (as long as it isn't oversized by more than 1.5x)
Get multiple proposals from multiple contractors, and multiple heat loss calculations. Or, hire a hydronic heating designer to do the heat loss calc and spec the boiler, then put it out to bid to several installers. There are many good boilers out there- most important to YOU would be how much available support & local expertise there is for the product, both at the installer and distributor level. You can have the greatest boiler in the world, but if something craps out in January and the local installer has to wait to call tech support in California who has to wait until the main office in Germany opens for business to order the part, who in turn then has to order the part from distribution in Japan, you've got a problem if you happen to live in Wisconsin, even if it's still under warranty and everybody is real nice about it.
To find competent installers it can be useful to find the local distributor for particular manufacturer and see if you can't get a short-list of installers from them. THEY know better than anyone who is installing them by the dozen, as well as who is calling tech support with stupid questions that are already answered in the manual, or should be part of general knowledge. (They won't be sending you to the latter. ;-) ) Mind you, the ability to install them competently is a different aspect than sizing them correctly. Those who insist on doing a heat loss calc using software that takes into account the wall & roof areas and R values, windows & doors etc. move to the head of the line. Those who respond positively when prompted to do a Manual-J (even if the charge you a few hundred to do the work) are at least on the consideration list. (There are a rare few who may offer to do a blower-door test to be sure to get the infiltration rates correct.) If all they want to know is how many square feet and want to throw out a number, move on- or it will end up costing you money in the end no matter what they charge you.
To assess any Manual-J calc, first look at the outside design temperature they used for the calc. Too often well intentioned people will use a design temp 10-15F lower than the ASHRAE 99% number for your location. (With a zip code I can probably look it up or estimate it from weatherspark.com weather data, or you can google the exact phrase "outside design temperature", along with the name of a decent sized city near you.) Most Manual-J methods end up oversizing by at least 20-30%, so even UNDERSIZING the boiler output by 10-15% has very low risk of leaving you cold, and is preferable to oversizing by 10% from both a comfort & efficiency point of view. Long burn times (and never short-cycling) are the hallmark of a right-sized and appropriately set up system, which will also have lower maintenance & longevity issues.