Hi, thanks for checking it out!
The weights came with the kit....it was added to the interior of the engine prior to closing the crankcase, and a little chunk under the ammunition bay. It certainly made the model feel more 'substantial' thereafter. It sits very nicely, with no indication of tipping.
The exhaust flame arresters were easy enough. I used Tamiya Weathering Master Drybrush over black base.
Cheers