The platforms were usually 2.5' from door sill to end beam, so figure an additional 5' over the length of the carbody for the entire car.
Coach #3 was ordered from Billmeyer and Smalls the same time as combine #18 to run on the Shade Gap branch. According to the roster in Rainey & Kyper's "East Broad Top," they are identical in size. Combine #18 came to the railroad without a clerestory roof, but I do not know if that was the case for coach #3. "Along the East Broad Top" has drawings for combine #18, so I would suggest taking height dimensions from that drawing. I'd let you know what they are, but my copy of that book is currently vacationing in a parallel universe, and my model of combine #18 is currently buried in a plastic travel case in my garage.
For Coach #5, the roster in "East Broad Top" lists the width as 8' 1", and a length over the carbody of 36' 8". I don't know that I've ever seen published drawings for coach #5. Adding to my consternation, the online index of Narrow Gauge Gazette magazines is not opening for me, so I can't check that archive to see. Argh!!!
Later,
K