Jeremy,
It has been a little while since I have posted on your build journal, and I read it from where I left off last. As far as a riveting tool, I have picked up two that were called "Rosie the Riveter" and I have used them on numerous projects since then. They were a little expensive, but they work like a dream. The only problem I have encountered while using them was trying to place rivets in areas that are close to a vertical panel such as an engine nacelle. But any of these riveting tools that use a roller wheel concept will have a similar problem. The ones called Rosie the Riveter come in various sizes and even offer a double or triple row tool should you be interested. I have been very happy with mine, and wish I had it when I was working on my 1/48 scale Monogram PBY Catalina several years ago.
I have never tried the marbling technique, but I must say yours is looking very good. I always manage to spray on too heavy of a coat when I do attempt to pre-shade a model, and this makes it practically useless for me. The one I did that turned out nice was a desert schemed He-111 in overall RLM 79...
Your Zero is looking very good, now that you are building a Nakajima built A6M, those Aotake colored wheel wells are looking very good. They also had a small white ring that went around the fuselage Hinomaru's...while the Mitsubishi planes did not. The Mitsubishi built planes had their wheel wells painted using the same color as the rest of the exterior, and the Nakajima built birds used Aotake here.
Here's a link to an article I wrote a while ago that goes into some the little differences between Nakajima and Mitsubishi built machines.
Random thoughts on Japanese colors. The Japanese A6M Zero…Part 1
Hope this helps, and you are really rocking your Zero... I love it.