David:
Yes, the gunner would just stand in that space - him and another guy (generally 2 folks back there for this gig, so far as I know, anyways). And yes, it will open things up for viewing. Do note that if you delete the pedestal, you should put a round cover-plate on the floor to "cover" its base hole...
Of course, while the kit instructions don't appear to address this, there MUST have been some provisions for ammo for that gun... The kit does provide a cute little ammo can and rounds, I think - but does not say where to put it? I would expect that there was more than one or 2 ammo cans stored in the car, so one needs to consider some rack or bin for these. I anticipate building some sort of rack for ammo cans inside...
As to radios... The radio set would have been in a frame mounted most likely on the left side of the car behind that driver's seat and behind the door-frame. Of course, for the complete set-up, there would have been maybe both a receiver and a transmitter, head-phones, antenna cable and junction-box (and, externally, the antenna mount and rod), and a power supply. Most of these rigs also had a loud-speaker hung or mounted somewhere. It is possible that the car carried only a receiver. I used the radio and power bits from a Tristar Pz.Kpfw 38(t) interior kit for my 223 funk interior. - Really nice radio frames and nice radios and bits! You could as well "borrow" a radio from any of many Dragon kits which may not be showing their commo goods in your build... The point here being that IF you decide you should have a radio-equipped 221 car, it will be visible if those turret "guts" are left out (even if they are installed, I think...). Of course, it is probably more than legit to make a frame (styrene rod and strips) and put a wood or plastic "dummy" in, and drape it with a "weather cover" with maybe only a head-phone cord coming out from beneath it...?
Let the builds ROLL!
Bob