I am intrigued as to the differences visible in N Gauge regarding these two locomotives.

Designed by R. A. Riddles and derived from Ivatt's LMS 2MT 2-6-0 locomotive design, itself a variation of Ivatt's Class 2 2-6-2T, the BR Standard Class 2 was the smallest of the BR standards and featured changes to the LMS design such as smaller cabs so that they could be used across the network where loading gauges were less generous. Darlington works was responsible for building the entire fleet of 65 engines and for a time construction of the LMS and BR designs overlapped. Like the LMS predecessor the BR design had a tender cab to enhance crew protection and visibility when running tender-first. Built as part of a batch of 10 destined for the Scottish Region.

Are the external looks unacceptable if substituting an Ivatt for a Standard?   

Quote from: GlenEglise on January 15, 2021, 12:59:37 AM
I am intrigued as to the differences visible in N Gauge regarding these two locomotives.

Designed by R. A. Riddles and derived from Ivatt's LMS 2MT 2-6-0 locomotive design, itself a variation of Ivatt's Class 2 2-6-2T, the BR Standard Class 2 was the smallest of the BR standards and featured changes to the LMS design such as smaller cabs so that they could be used across the network where loading gauges were less generous. Darlington works was responsible for building the entire fleet of 65 engines and for a time construction of the LMS and BR designs overlapped. Like the LMS predecessor the BR design had a tender cab to enhance crew protection and visibility when running tender-first. Built as part of a batch of 10 destined for the Scottish Region.

Are the external looks unacceptable if substituting an Ivatt for a Standard?   

A quick glance at some photos for comparison reveals (to me) five principle differences in appearance;

1) The bottom front "corner" of the cab was rounded on the Ivatts, angled on the Standards - probably not too noticable.
2) The step from the running plate down to the front was open on the Ivatts, closed with a sloped plate on the Standards - pretty noticable, to me at any rate.
3) The The steps up to the footplate and front running plate were an open frame on the Ivatts, a plate with steps rivetted/welded to them (and large holes cut out on the tender footplate steps) on the Standards - probably not too noticable unless one is fussy.
4) The top feed clacks were covered with a large domed rectangular plan cover on the Ivatts, left uncovered on the Standards - a dead giveaway, I think.
5) The tender axleboxes were plain bearings with an oilbath and wick lubrication on the Ivatts, Timken roller bearings with round covers, usually painted yellow, on the Standards - another giveaway unless heavily weathered to tone down, or conceal the lack of, the yellow covers.

In addition, pipework down the LH side of the boiler was uncovered on the Ivatts and boxed in on the Standards.

Up to you as to whether those differences are significant enough to concern you, I'd say that the top feeds, running plate step and tender axleboxes are.

The biggest difference was that the standards weren't DCC ready, whereas most of the Ivatts had a chip in the tender. Very conservative for the usually forward-thinking Riddles!

I'm not so sure about the tender axleboxes from new.

Certainly by approx 1964 they were yellow, but photos-unfortunately mainly black and white-seem to show that as built they were black.

Certainly, as new, Britannias were black and only painted yellow post 1960ish. The earliest dated colour photo I have of Britannias with yellow axleboxes is 1961; some may not even have been done before withdrawal.

Martyn

I had to check photos to make sure I remembered right, but the biggest visual difference to me is that the BR version's cab tapers in from bottom to top while the LMS version is upright. Quite noticeable when you compare them.

Dave

Funny we were talking about a conversion the other day, Dave!

Martyn

Over to you on that one!

Dave

What chances of an RTR BR Standard 2MT then?

Or suitable alterations being made by some other means?

It probably no coincidence that for the class 2, we have the LMS but not the BR equivalent while for the class 4 we have the opposite. In both cases, while mechanically near enough identical, there are many visual cosmetic differences, but possibly not sufficiently different for the RTR manufacturers to have confidence that enough would sell...
Probably the most likely route to a BR 2MT will be a 3D print body to fit the Ivatt chassis.

As to the original question if whether it is an "acceptable substitute", that is down to the individual opinion. I'm not sure if you mean to renumber an Ivatt as a Standard, or simply run it in place of a Standard? For me, I wouldn't do the former, but I'm sure the latter must have happened for real from time to time...