Thank you for that. I think that the difficulty that you are having with the alignment is at least partly in your .dat files, but might also be in your .blends. I have modified your Class 101 .blend files (modified versions in my Github archive) and produced multiple livery variants of them (in my Pak128.Britain-Ex Github archive). In so doing, I noticed that the vehicles were all facing top to bottom when initially exported, and I had to rotate the camera and lighting dome by 45 degrees in order to get them to the correct starting point, which is facing top right to bottom left.
Secondly, you might notice that the .blend files that I produce for graphics that have been automatically exported in this way all have a particular ordering of the graphics which is different to the ordering of the graphics for manually aligned sets. See here
for the example, using the modified version of your Class 101 .blends. The image definition for the DMBS is as follows:
Note the sequence: 1.4, 1.5, 1.6, 1.7, 1.0, 1.1, 1.2 and 1.3 with E, SE, S, SW, W, NW N and NE. Manually aligned graphics have a different sequence:
The sequence of the ordinal directions is the same, but the images for this manually aligned graphic are in a straight sequence of 1.0, 1.1, 1.2. 1.3, 1.4, 1.5, 1.6 and 1.7. If you use this straight sequence with an automatically rendered/aligned vehicle, then it will be turned through 180 degrees and not properly aligned, which I suspect is the problem that you are having with your NER Tyneside units. Might I suggest that you have another go with the NER Tyneside units using this modified sequence to see whether that helps?
As to the Leader class, that is a very unusual locomotive indeed! I notice that you have depicted it in the photographic grey livery in which it actually ran: do you not think that it would be better to depict it in the black livery that it would have worn had it ever gone into production?
As to how to calculate the power of a steam locomotive, you should use this
spreadsheet, which is what I have used to calculate the power of all of the steam locomotives in the pakset (for 0.9.0 - this was not done for the release of 0.8.4). To calculate the tractive effort if you do not have access to that datum directly (most 20th century steam locomotives have published tractive effort figures somewhere), use this
website (which also purports to give power calculations, but these seem to be wildly inaccurate, so ignore them, and use the spreadsheet instead). Looking at the Wikipedia article, however, the tractive effort is given for this locomotive. As for the top speed, note that it was intended to be a replacement for the LSWR M7 class, which was a suburban tank engine, so I should not imagine that it was intended to go much faster than about 130km/h, although I stand to be corrected if anyone knows better from the operational reports.