Well Ray, your comments have turned my fear of 707 pylons into a fear of 707 engines. I had heard the same thing about the Roden JT3Ds. So I thought I'd run an empirical test. Here are all the JT3C and JT3Ds I can lay my hands on immediately, I also have a set of white metal JT3Cs around here somewhere but they lack half way decent pylons. From the right: the Roden kit JT3C, the Authentic JT3C , the Roden kit JT3D, Welsh Models JT3D (from their 720 kit), the Minicraft JT3D (from their 707-320B kit) and the Contrails JT3D.
The first thing to note is that any resemblance between a JT3D and the Contrails version is purely coincidental, particularly the front fan housing which is vastly too long. This is a nuisance since I bought three sets of these engines to make my 707-328s - If anyone wants them despite their mutant appearance I can let them have them for free. Better in your house than mine.
The Welsh Models JT3D is a tad smaller than the Minicraft or Roden JT3Ds. The Welsh Models JT3Ds might be more accurate in terms of size but you can only get them by buying their complete 720B kit, which is not cheap. This leaves only the Roden and Minicraft JT3Ds and since they are of a similar size I'd guess they are close to being accurate - it would be hard for two companies to make the same mistake (unless Roden stole the sizing from Minicraft). Of the two I slightly prefer the Roden JT3Ds, but I don't know that you'd notice the difference on the kit.
So, Ray, I can let you have my spare Roden JT3Cs, though I don't know that you really want to use them. Welsh Models offer JT3Cs which might be better, but if you don't mind the size difference let me have your snail mail address and I will send them on to you.
It looks like I'm stuck with the Minicraft JT3Ds but the trouble is that I have three Minicraft 707s with three different engines - a 707-300 with JT4s and a 707-400 with Conways. However, I need three sets of JT3D enigines. After my experience with Authentic's JT3Cs I'd be happy if they offered JT3Ds, but they don't. So if anyone out there had spare sets of Minicraft JT3Ds they don't need, you can make me a happy modeller.
Leigh