Miss Prism

That's a Collett 3500g. I have not seen a pic of a Saint with a Collett 4000g. Some Saints (mainly Scotts) ran with Dean 4000g units in their early years.

Body wobble is a common phenomenon on many RTR bogie coaches. The cause of the oscillation is a combination of bogie hunting (more apparent on straight track) and the lack of secondary (i.e. bogie to body) springing. The interface between bogie and body at the bogie pivot point is also an important factor. 10 years ago, CLAG took some video comparisons to examine the issue, the guinea pig being a Bachmann MkI. The video confirmed the roll plane frequency of the oscillation reduced considerably when secondary springing was present. (Unfortunately, we never uploaded the video because we felt a more thorough examination was needed before publishing any quantified conclusions. And then time moved on.)

Preservationists seem fond of red reverser handles and regulators. Is that wrong? Or was there a change from unpainted to red at some stage?

Looks white to me, or am I getting confused? (More than possible!)

When you say 'shake', do you mean wobble from side to side?

SRM 63 in what is thought to be brown livery. (There was an RMweb discussion about this somewhere, iirc.) It retains its below-waist panelling. The Kernow has below-waist panelling, because that is what the preserved 93 has. It's engine compartment windows have been updated. (Again, like the preserved 93, although the prototype 93 never had the early-style windows.) It has an original low bunker. Here is 63, later, in crimson lake. Date unknown. All its below-waist panelling has gone. Bunker state unknown. Front sandboxes are not yet in front of the bogie frame. My guess is c 1920.

I can't find any evidence of whistle shields.

I think that's Castle 100 A1 Lloyds on a running-in turn. (BTM to Swindon?)

Yes. When the filler moved forward on later (3-segment or 5.5 segment) tanks, front steps and a higher handrail were fitted. Here's 1874, still with old-style lamp spigots, but post-1904 when it got this S4 boiler. (It was panniered in 1912.) Looks like Weymouth.

The most contentious area of saddle tank design is the tank cross-section. Judging by the build span (1890-5), I am reasonably sure the 1854 saddle cabs were 8' wide, but I've have not seen a good end elevation for the class, and the saddle tank end elevations that do exist do not match most of the 1854/2721 photographic evidence. These two pics show how much narrower the 1854 tanks were than the cabs. I would estimate these tanks are 7'2" wide. That said, it's probably certain that some 1854 locos ran with different width tanks at various times. There was considerable variation in cab fronts on saddle tanks, even within the same class. Note the extra large spectacles on 1736 (at Laira, 1904). 1873 has a short tank, an old-style cylinder cover and an early injector.

Thanks for pointing to the 1752 pic - I had overlooked that one!

http://www.gwr.org.uk/liveriesuniforms.html

Milk, horses and passengers.

There should be a handrail on the footplate between (side elevation) the front and middle splashers.

I think the front tank step came in with the '5 and a half' segment (extended) tanks, and these date back quite a way. (Not sure exactly when.)

I don't think Rapido is suggesting the O18s appeared in black. (If I've understood your point correctly.)

The O24 was the first RCH brake design. On the O24 body however, the corner plates extend over the curb rail. (Unlike the O18.)

I can't find any evidence of a front tank step on a 5-segment 1854.

The lid on the top of the sandbox should be an ellipse, not a rectangle.

Injector (albeit a modern one)

The rectangular base of the tank lifting rings should be a lot smaller. See http://www.gwr.org.uk/pannier-pics/pannier-topfeed2.jpg Edit: as you were, some of the early ones were as you have drawn.

The cylinder section of the filler should follow the radius of the tank. This convention may however be a modern (say post-1890) feature.

The dome needs a bit of tweaking I feel. The radius to the tanktop needs to change around the base perimeter. This radius in end elevation should be larger than the radius in side elevation.

The O18 is a good choice, straddling two eras. It was the final DCIII open, and the first to have a sack-truck door.

56xx and 57xx wheels were different. The front of the boss of a 56xx sticks out further than that of the 57xx, i.e. the wheel is thicker at the boss. Not sure why this was - strength presumably. Visually, it is not an obvious difference.