It’s a quick fix for small scale modelling but unpicking your work if unhappy with it may be problematic. Using solder allows for ‘tacking’ pieces in place with small solder joints to check the fit before soldering solid. The chassis is not something to be scared of. Get one of these and it will keep you square: http://www.poppyswoodtech.co.uk/tools.html
Might be worth checking the back to back as a first step. Gold standard fix is some kind of flexi chassis as identified above, but flangeless wheels are an easy fix. 6 w coaches can be curious beasts and and require a bit of fettling to get round the track…
The Pullmans had standard Pullman design bogies, apparently constructed by the LMS , who presumably had more experience than most UK concerns in building 5’3” bogie stock…..
A handsome and interesting engine. Found to be too heavy so was rebuilt as an 0-6-0 tender engine. Lasted until 1950. Looking into this topic shows that the often overlooked DWWR/DSER had some lovely designs, and some particularly charming small tanks.
Murphy was an interesting character himself. I knew about his press and political career, but not his railway work….https://en.m.wikipedia.org/wiki/William_Martin_Murphy
Excellent news - well done! Halfords grey plastic primer or its equivalent will do just fine.https://www.halfords.ie/motoring/paints-body-repair/primer/halfords-primer-grey-500ml-473116.html