Best Of

You're making it a good deal harder than you need it to be. The crossover trap I suggested takes care of the venting. The loop seal takes care of the condensate.

Now that loop seal has to be proportioned to the expected maximum steam pressure, or steam in the main will happily blow through it and get into the return. This you do not want.

Now you could also go the F&T route. A lot more maintenance and expense, but as you please. Be sure to use a small enough one — the usual error with an F&T is to make it too big. There isn't all that much condensate. Note that an F&T is NOT an adequate substitute for a main vent, so you will need to put a main vent at the end of that main if you choose to go that route.

I presume the dry return is vented somewhere? Like near the boiler?

More or less as @delcrossv suggested. Use that 3/4 inch stub, right angle to inlet of standard radiator steam trap, come out of the bottom outlet of that and down to the level of the dry return without that existing trap and drop. From somewhere convenient before that existing trap, go all the way down to the floor, come back up for your loop seal and tie into the dry return with the line from the nice new radiator trap.

Use the existing trap for a doorstop.

I have mine set to 2 CPH which goes against Honeywell’s recommendation of 1 CPH for steam however after straightening out my main venting I began experimenting (3 was causing rapid cycling and I became concerned but when I went to 2 things smoothed out)

In my opinion and I’m sure some will disagree, but I am trying to balance comfort with economy and the 2 CPH keeps the house warmer and it runs about 20-25 minutes and shuts off, some may debate the increased cycles and it should run longer at each interval.

I have 3 remote sensors and they work great. I have setbacks as well and the t-stat stops the boiler just prior to reaching setpoint (3 sensors in average) to allow the room to go past the desired room temp.