I just found your post while looking for something else. I tried to reply on my phone last night but the only thing it did was to move this post to the top of my list???
Anyway, I have used a Dragon Models 15/25motor which fits without having to cut the other end shaft. They make a 15/35 which is very powerful and with the shaft cut may be the same length but the curvature of the tank may be a problem. Ragstone Models are reintroducing the Agenoria range on behalf of Mike Williams and may help you with the castings if you ask them nicely. My 679 is virtually complete and in Dai the Paint's ststu
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