In order for the boiler to produce much condensate (and get full condensing efficiency out of it) the water returning water from the baseboard has to be entering the boiler at temps significantly below 125F (the very beginning of condensing.) That generally takes an output temp under 140F or lower.
Set the thermostat up to run at a constant temp, and keep lowering the K-factor until it either doesn't quite keep up, or it starts short-cycling. Then bump it back up one notch.
The min-fire output of the -180 ASME is about 16,000BTU/hr, so it will balance perfectly with your 80' zone at 200 BTU/ft, which happens when the output temp of the Navien is about 125F, (returning water about 115F) which is good- it won't short-cycle at temps well into the condensing range.
But the other zone could be an issue. According to the manual , with an entering temp of 140F the Myson only delivers ~6000BTU/hr, and that's at the higher blower speed. You may need to upgrade the radiation on that zone to take full condensing advantage, but see how it goes. When you bump the K-factor down so that you're guaranteed to have output around 130F, turn the Zone-1 T-stat way down (or off) on the other zone, and time the burns with just zone-2 calling for heat. If it's under 1 minute with 130F output on the boiler it's a problem but if it's 3+ minutes, you're fine.
All good solutions start with a heat load analysis, and we're kinda shooting in the dark here. A typical 1990s code-min 2-story comes in with a heat load at 0F at about 15BTU/foot. The 99% outside design temp for Windor Locks is +8F, so all things being equal ~13BTU/foot might be a middle-of-the road WAG, which would imply a load of about 27,000BTU/hr. Depending on how much of the raised ranch is below grade, and the depth of the cantilevers it could vary by quite a bit from that crummy rule-of-thumb approach, it's probably not more than 35K worst-case, and it could be close to 20K.
If it turns out to be close to the 27KBTU/hr number you should be able to run in condensing mode literally all the time and still keep up (without short-cycling) on the fin-tube zone, so that K-factor can probably be dropped by quite a bit- be pretty aggressive in your initial adjustments. (At 130F AWT you'll get over 20,000 BTU/hr out of 80' of fin-tube, which is MOST of your heat load.)