Actually you don't have to knock out the entire seam there on the turret. I think the real turret was built from two large cast pieces, a top and a bottom and they were welded together along the seam line in the real thing. So you don't have to get entirely rid of it, just make it look like a weld seam. Or that's how it looks to me anyhow!
I found a bunch of photos in this walkaround while looking for a good close-up of the turret:
http://www.primeportal.net/apc/robert_de_craecker/t17e1_staghound_scout_car/index.php?Page=2