I'm not sure if the new SGU uses this solution for Morrowind for 5040x1050...
Open up mw_fps_opt.ini located in the Morrowind directory. You obviously have to have the FPS optimizer installed.
Under the heading [misc2page] are the FOV and FOV aspect variables. Set the FOV to 140 and the FOV aspect to 0.20 (I think using 3840x1024 these are set to 133 and 0.25 respectively).
Save and exit and voila, Morrowind at correct aspect and FOV.
NB. As always you can alter the FOV to suit but 140 seems ok to me.

An old but great game. Modded correctly, looks better than Oblivion and plays 20 times better. Anyone still playing it, hope this helps. Paddy, if this is already in the SGU info, or is just common knowledge somewhere else on the site, feel free to delete this post.
Edited for numptiness...