If..........
.....You have a hot boiler that is cycling and cold pipes you have a circulation problem....as in no circulation at all.
This could be due to the pump or it could be due to an air lock in your zone piping somewhere.
.....
You have a hot boiler that is cycling and hot pipes that get a
lot cooler on the return flow,
again, a circulation problem but in this scenario you are getting a very small amount of flow
and again this could be the pump or an air lock..
You have hot supply pipes, a cycling boiler AND hot return pipes that are nearly the same temp as the supply,
You have a problem with heat transmission out in your zones. This can be from dust accumulated on the BOTTOM of the fin tubes, or
furniture that is moved up tight to the baseboard, or curtains blocking air flow etc. The issue being heat is available but the baseboard is not shedding it out in your living space.
All that being said.....
Most residential pumps have a standard 6-1/2" flange to flange spacing regardless of brand or size. Your 111 is a different beast being that it is a coupled pump (separate motor, center bearing assembly and the the impellor and housing assembly).
You should be able to buy an impellor at a plumbing supply house. It's not an item you will find at a big box store. I can get one for you if you have trouble finding one.
That 111 is designed to move a LOT of water at pretty low head (flow resistance). which means the piping around your boiler and the baseboard piping itself should be pretty significant in size. 1-1/4" at least. Even for the zone piping.
If you have normal 3/4" copper fin tube baseboard, I'd have to say that chances are very good the 111 is a totally wrong choice for your system's circulator.
You can see what that series of pump is made to do at the link here... Click on "catalogs" then "in line circulators"
http://www.taco-hvac.com/en/products/110-120 Series In-Line Circulators/products.html?current_category=197#
I have a couple fairly new ones in my shop that were taken off a boiler replacement job but I don't remember what exact model they were.....seems like 112 maybe....
That style of pump is not used much any more except in large commercial applications. The wet rotor variety has pretty much overtaken anything 50GPM and below.
You would definitely have to change some piping to fir up a pump like the others here are talking about.