Welcome to the forum, Eric.
I have added your two tractors to the Trusty Register but you won’t see them on the website listing until I’ve been to look up the numbers. With lockdown as it is I don’t know when that will be, but keep checking and eventually we’ll get there.
What I can tell you is that 3952T was sold in February 1945 and 6657G was sold in July 1946. This was a period when they were fitting a lot of lend/lease American engines because they couldn’t get hold of the British ones. The later tractor was probably just using up stocks of these engines before the factory went back to JAP and Douglas engines.
The question you ask about the throttle rotation can’t be answered easily as it’s a matter of preference. I’ve seen both on the tractors that I’ve collected but it would make sense to change them so that they both work the same way. To change the direction simply slacken off two of the four bolts on the throttle rod joiner (usually alongside the toolbox on the outside of the right hand side of the tractor). You can then turn the rod through 180 degrees and then tighten the bolts again; you will find that you’ve changed it from clockwise to anti-clockwise rotation (or vice-versa) in a couple of minutes.
Best of luck with them.
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