Here's the plan:
1) Slave the old boiler into the primary loop. Winter time demand calls will then have ~52 gallons of 185f water to draw on through the secondary loop, thereby assuring that the radiators get enough hot water to bring the house temp up to tstat quickly, and that there will never be a problem with the boiler getting slammed with cold water.
2) Install a valved loop inside the primary that will bypass the old boiler during the summer time. That will reduce the heated mass in the summer time and save me some coal in the process.
Cost: 1 circulator, 4 valves, 3 radiator valves, some pipe and a days worth of work. Or two....