Thanks Nigel, Paul & Rick! I've been making slow progress on several aspects of the build these past few days.
The Bristol engine assemblies have the exhaust accumulator rings at the front, and I've seen these called out in many bright colours in the past. Wartime photos have all kinds of weathered looks to these areas - and if you are lucky enough to find a "genuine" colour photo from that period it can be helpful in determining how to paint them. I chose to mask off the black/dark earth/green camo first, then airbrush the rings with Alclad II Brass, followed with a gentle, diluted airbrushing of a Tamiya acrylic mix of smoke, NATO black and a touch of brown.
I had never applied a black underside to a model before, and studied a few on-line builds as how best to emulate a weathered look to it. experimenting on some spare parts first, the process I used was to airbrush on a base coat of NATO black, protect it with a fine gloss coat, then add some small patches of XF-63 German Grey on the many panels. After again protecting this with gloss, I added a medium grey mix of oil paint thinned with mineral spirits to the surface detail (and the engraved panel lines and rivet detail is very nicely done on this kit). After about 45 minutes I wiped this off using a cotton bud. Pleased with my experimental results, I went ahead on the model working in small sections at a time.
To complete the underside before I begin on the upper surfaces, I tried to add the stencil markings using the 1ManArmy mask set. I'm absolutely amazed at how well these stencils work at that scale. I had used the 1/32 Spitfire set previously...but wasn't sure how well the 1/48 lettering would appear by utilizing these tiny masks. Fifty bucks well spent...so far

Cheers!
DSC_3275c_01 by
Gary Edmundson, on Flickr
The bright Alclad brass on the right...toned down with a dark acrylic Tamiya mix on the left.
DSC_3278c_01 by
Gary Edmundson, on Flickr
NATO black was washed with a grey oil paint to bring out the fine detail of the kit's lower surfaces.
DSC_3289c_01 by
Gary Edmundson, on Flickr
The 1ManArmy masks applied for the underside stencils, painted with an off-white.