Hi Jamie,
it would appear you have already gone through the same process as I'm going through. As far as the Class 117 to 114 conversion, I'm initially looking at using the etches as overlays rather than as a pure etch as it will give some stability to the sides, even though I'll need to hack some of the windows out.
The class 110 is a bit of a slow burner at the moment as each time I look at my photos I begin to notice more and more additional bits and pieces I need to add e.g. horns below the buffers, replacing moulded water pipes, the buffers themselves definitely need replacing!
As far as the drive units are concerned, I've already got a replica one and fully appreciate the height issue, so I'm still thinking of replacing the existing motor with a CD/DVD motor and then DCC it to give better control. I figure for the price of the motor, it won't really be that much of a waste of money if it doesn't work out.
I don't intend starting the Class 124 TPU until later in the year as I really want to get the other stack of projects out of the way first. I'm in the process of trying to get a lot of the bits and pieces I will need to make a start, so the photos will be really useful, haven't had chance to go through them all yet, but thanks very much. You've obviously made a better start as you've already got the bogies sorted, everything I've researched so far indicate that the Trix ones are to scale and the best available.
I'll try and get some photos taken of the etches over the weekend so you can have a look at them.