@Stefan The louvers have little tabs that fit in the notches in the back of the grill. I attached them with some Gator Glue and they've all held up except for the top one, which I managed to knock loose tonight. I'll take a picture tomorrow to show.
@John K You shouldn't have to file them. The notches in the back of the grill fit perfect (at least on my M16, but the grill is the same for all DML halftrack variants) and you want to angle them about 45 degrees downward. That should take a bit of the bend out as well.
I finally got my RB barrels in for the quad .50cal mount. They aren't bad (not the best) but at $4.99 a piece, I could replace the entire set of 4 for less than the price of some of the other replacement barrels.
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I ended up not using any of the PE parts, as these aren't the normal M2, nor did I use the cocking lever or the rear handles, but I'll save them for future builds, especially if I use a Tamiya M2 for the base, as they aren't too bad for plastic. Cutting free the plastic barrel was more tedious than a normal M2 as the front mounting post extends below the cooling jacket and barrel. Careful cutting with the snips and some scraping and I got them cleaned up decently.
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They are a marked improvement over the kit guns, and as they are pretty much the central part of this build, spending a little extra was worth it.
Some dry fit test photos (only got one side done tonight):
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Mated to the chassis, dry fit for photo purposes with the front cab and grill (how I popped the top louver loose):
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That's all for tonight. Tomorrow I should be getting my Atak Zimmerit for the Panther campaign, so I can continue on that for a bit.