The original was a compound loco, with two outside ones being LP.
If you take original 19" dia and scale it down 1:22,6 it would be .841"
Evans actually made them .750".
...cylinder casting juts out from the frames so much (appx 6 to 8mm)...
I am not sure I understand you?
Drag and buffer beam are 4 3/4" wide
Frames outside 2 1/8" wide
Cylinder outside from frames 1 3/8
So cylinders on the outside are 4 7/8"
I make it sticking out by 1/16" [1.6mm] both sides - total 1/8" [3.2mm]
Having said all this
I do not disagree with you - it would look better/more proportional with smaller cylinder.
...2.5 design was designed to be a people hauler and as such the clearances are generous...
Do you mean loading gauge?
Apart from the fact that your usual 2 1/2" design is usually more freelance than scale
I thought there very much similar?
BTW, Eagle being freelance version of class V, you might be interested in the last loco built for GNR(I) in 1948.
This is simple (non-compound) 3 cylinder class VS with Walschaert outside (and inside) valve gear.
Much nicer looking as well
It shared most of the with V class,