Miss Prism

The drawings in P_044.pdf are good enough to scale from, and will provide reasonable sizes for the other styles.

At Southall

I don't think so.

First instance of plated over portholes I know of is June 1924 (on a Duke). I think Johnster has got the reason right - except for early high-cabfloored locos (e.g. Counties, Saints, Stars), the portholes weren't particularly accessible. Also, they were in the 'drifting smoke line', so would have required regular cleaning.

The roof looks far too high to me, (Too small a radius.) And I've never worked out what kind of accommodation or function took place underneath the larger tanks

You'll have to find that out by trial and error on your particular coach lengths. They'll look silly on straight track of course.

Yep.

You'll need extra long 3-link couplings on that kind of radius with non-sprung buffers.

There are no rods, so the axles need only be approximately 'lined up'. Within 0.5mm would be fine.

If you fancy a CSB plot for LNER group standard tender Have a look at how simple a sprung Brassmasters tender can be

http://www.gwr.org.uk/pannier-pics/pannier-top-detail.jpg

I suspect this 1947 pic of 56875 might have been Hornby's inspiration.

https://www.rmweb.co.uk/community/index.php?/topic/34065-dart-castings-gwr-aa3-road-van/

Advocating that manufacturers should send swatches of known colour systems such as RAL to their factories sounds fine and dandy, but there's only one slight snag. They don't do it. There are plenty of online colour converters (e.g. rgb to hex, RAL, CYMK, NCS, Pantone etc), so rgb is as good a colour language as another. Note though that RAL is a limited range, and the nearest r79 g45 b36 (for example) comes to is RAL 8016 'mahogany brown', which RAL describe as 'close but distinguishable'. The issue of monitor variation is very valid, but the nub of the matter is that in terms of talking to each other, whether it is modellers here on a forum, or manufacturers trying to communicate with a factory, 'r79 g45 b36' provides a far better means for a more informed and objective discussion than "well, it's a sort of mahogany brown".

That caveat is on the page. If anyone has the 1990 Addendum, I would appreciate a copy. Ideally, I would like to hand the page on to the LSWR Circle to get it sorted out properly.