Connecting two steam boilers together

LJR

I currently have a Weil Mclain 872 steam boiler. This has a 6 inch header that is feed by two taps in the top of the boiler. This feeds about 1060 sq feet of steam radiators. In the winter we use only 527 sq ft of radiation. The header has a 2.5 inch capped off tap. This steam boiler works great.
I also have a EFM Coal Stoker 700 with a three inch tap. I was going to pipe a henderson loop and all close boiler piping and controls as per the manual for this efm. The steam will then be feed into the capped tap which I am going to flange to 3 inch. Condensate will return via existing wet returns.
The oilfired Weil Mclain will only run if I am going away or the coal goes out
The water lines will both be at the same height.
Any suggestions as to what to valve off and what not to?
Will I flood thwe weil Mclain with the condensate?

bob young

Don't forget the vacuum breakers