Mark,
For your next(?) replica, you might want to use a pre-´66 chassis, as it basically has the same dimensions as the wartime chassis (notably tread), and will give you the 5-stud drums + wheels.
Anyway, this one really looks the part! Only thing I wonder is you might have to lengthen the mudguards to run all along the length of the hull, as this might improve stability in the water?
Keep up the good work!
Hanno