I found those New Irish Lines articles I mentioned previously.
The first is on the proposed dieselisation of the GNR, which includes a number of drawings of proposed loco designs from the likes of Beyer Peacock, Alsthom, Sulzer, Henschel, Deutz, Vulcan Foundry...
'Great Northern Railway Diesels That Could Have Been' by Dónal Murray
Part 1: https://www.dropbox.com/s/mz86b7x52bf58oh/New%20Irish%20Lines%20-%20Vol.%204%20No.%202%20-%202005%20November.pdf
Part 2: https://www.dropbox.com/s/7y7ar7ocv92l0aa/New%20Irish%20Lines%20-%20Vol.%204%20No.%203%20-%202006%20May.pdf
(Incidentally, the latter issue also includes an article by one J Beaumont entitled 'CIÉ & IÉ Liveries' - there's no escape!)
Dónal's articles prompted a follow-on from one of our own members in the May 2007 edition...
'The GNR diesels proposal: an antipodean perspective' by John Mayne
https://www.dropbox.com/s/f04ck64yjj6u9k9/New%20Irish%20Lines%20-%20Vol.%204%20No.%205%20-%202007%20May.pdf
And Dónal also wrote a piece on the proposed electrification of the GNR main line, which includes a couple of drawings:
'Proposed Electrification of the GNR(I) Main Line'
https://www.dropbox.com/s/37ilc0r6lk4brg6/New%20Irish%20Lines%20-%20Vol.%204%20No.%206%20-%202007%20November.pdf