House was built in 1951 with a walk-out basement. The man-door that leads from the basement to the outside needs to be moved/replaced, since framing/insulation have been added to the interior block walls. This requires the door be moved 5 inches inward toward the basement, to be flush with the newly-framed inside walls.

The original jambs look like they were made from 2×10’s, and are rabbeted. They are about 9.5 inches wide, to span from the original inside block walls to the outer brick face.

So now, the total distance to span with the jambs is 9.5 + 5 = 14.5 inches.

There is also a storm door flush to the brick that I want to replace.

Current door is 36×80. Door opening in the masonry is  39 11/16 wide and 83 1/2 high.

What’s the best way to frame this 14.5 inch deep opening in the wall?  Would it be best to try to duplicate the original construction, namely to build two separate jambs out of 2×6’s, one for the inside door and one for the exterior (storm) door, and just fill in trim between them? Or else span the entire 14.5 depth with 3/4 plywood (exterior-grade) all around, and use a pre-hung door on the interior?
 
Thanks for any suggestions.