That layout looks fine. You'll have to be able to adjust the port lengths on a prototype, when tuning it. That's easier with tubes - how will you do the adjustment with shelf ports?
Tha A port probably should have a smaller area than you've got there. In my Akabak model you'll see I made it narrower.
The C port can be square. But I suspect it'll just end up being a hole in the baffle, with no actual tube required. In which case any shape is easy (it can be tuned by enlarging the hole).
Ars est celare artem
