Will the mini-ducted split sez-kd09na4 (or something similar) physically fit and operate in my knee wall attic which I will encapsulate?

Mitsubishi SEZ-KD09NA4 Dimensions:

31 ⅛” x 27 9/16” x 7 ⅞” 
(pair with SUZ-KA09NAHZ)

Kneewall door dimensions:

28.5” x 39.5”

Knee wall attic: 

42” x 42” from wall to rafters and floor joist to roof rafter

1915 1.5Fl Bungalow 1622sqft not including basement outside of Boston (Zone 5). Loads in my 2nd floor are very low especially our nursery and the nursery is likely too small for the FH06 wall unit even with 1:1 outdoor unit. (Would like to avoid doors open all night or transfer grills). Will remove the cellulose and likely encapsulate with a combination of HFO CCSF and OCSF for hopefully R49 covering rafters to reduce thermal bridging.

Heating/Cooling Loads:

Master: 7860/3130

Nursery: 3849/1542

Stairs; 76/59