Success! But for those interested and that have been following, I'll walk thru the process:
Now that the Brass is Prepared (making sure we have everything joined to a 'fret' and all frets joined to a 'backbone', so we dont lose them in the etchant), we need our etching tank. This may sound high tech, but I ran with the SAME set-up I have used to make PCB's - a rectangular chinese dish sitting in a metal baking tin. Into the tine we pour some hot water - maybe an inch or two - then into chinese dish, we pour 5 parts hot water, followed by one part Ammonium Persulphate. ALWAYS ADD CRYSTALS TO WATER, not the other way round... As benign as Ammonium Persulphate sounds (and is, with respect to etchants), it will seriously hurt you if you treat it with contempt, especially if you decide to splash it in your eyes or take a sip. DONT DO ANY THING DUMB, take your time and if you are worried, wear goggles and latex gloves. Once you're used to it, its no different that handling say Lawn Weed Killer or something... Now mix the crystals until the totally dissolve.
Clip something onto your prepared brass and fully submerge it into the etchant. This is my spectacularly complex and high-tech looking setup:
Regularly agitate the etchant - I just stir it for a minimum of 20-30sec each minute, and in this case, I was flipping the brass over every few minutes. The reason I use a metal tin is so I can use that to monitor temp; 70-80degC is uncomfortable to touch, but doesnt instantly burn. If you can comfortably touch it, you temp is probably down to 50degC or so, thus add more hot water to bring the temp back up... Once things are going, you'll notice the etchant start to gain a blue-green hue and a close look (DONT GET TOO CLOSE - remember your EYES!!!!) will reveal bubbles. The Blue-green is the copper being dissolved out of the Brass Alloy and the bubbles I believe are excess oxygen from the reaction. As the Brass reacts, it begins to take on a lighter, duller look; see...
... as things progress, you'll get to the point where the etchant eating through one side of the brass, reaches the etchant eating at the other side; this means you're all but there. The below photo shows about the 5 minute mark - you'll notice just how effective my ordinary 'Staedtler Lumocolor CD/DVD' marker pen actually is, but any water proof permanent marker should suffice. This perfectly illustrates the repairs to frets and parts, as well as the extra fretting added between each part fret and the 'sticky-tape' backbone. What you're looking at in the back of the mounting arms and Cowling Braces (x3) and the front of the radiator flap actuator mounting ring - and some flaky looking brass!
Once you can see through the places where there is NO pattern on either side PULL IT OUT. If you've properly agitated, the etching should have been nice and uniform. In my case, I was slightly premature in removal as one side of the actuator ring still has a THIN sliver of brass where it shouldnt be (left side, between a brace and an arm) - I also lost two small legs on the ends of the short cowling support braces, but that was likely due to them being too thing - anything you draw should really be a minimum of 2.5 - 3 times the thickness of the brass. Still, here is the result:
Now, close looks will reveal the front and back are misaligned by some 0.2 mm, but to put things into perspective, the Actuator Ring is only about 13mm across, so the parts you're seeing a REALLY SMALL - the Cowling Braces (such as the long 'thing' under the pair of engine mounts) are only 1.0 mm wide, the largest bits (Mounting Arms) are about 23mm long!
So? Thoughts? Obversations? Questions? Next will be to try and use the Mounting Arms (well, I guess they're mounting arm faces) to create the correct width of arm...
Dan