A standard installation will include expensive circulator pump isolation flanges
I think one of the reasons for efm not putting circulators on the supply side was because the outlet of a 520 boiler is 3" and the largest flange we handled was 1 1/2". I will ask about this issue and get back to you.
ISO flanges are cheap. When you consider that replacing a pump without draining and bleeding the system is a 10 minute process, the $50 cost (?) is worth it. I have ISO and ball valves everywhere I would need to ever work on my system.
Another reason for the bypass loop is that you can force some of the cooler water back into the supply line to moderate the heat to the radiators for longer runs on a single loop system, where the tstat might be in the first room. I think the boiler holds 39 gallons of water, so it also moderates the whole boiler.