Half height video card, 320W power supply and must draw power from the slot.
these are the limits you must stay under. the 750TI calls for a 400W power supply, it may work it may not. I wouldn't risk it.
will work: gt 730, gt 610, on the nvidia side. both will work, if available in Half height, with a 300W power supply. IDK how they game
on the AMD Side we have the HD 4550 beyond this they require 400W minimum PSU's
http://www.game-debate.com/games/index.php?g_id=1308&game=Grand%20Theft%20Auto%20V GTAV sys req
that power supply would seem to be proprietary/not readily available. it also has non standard power plugs which rules out a new case, power supply, and powerful GPU.
does your power supply look like this?
http://www.dappz.com/images/computer_parts/508151-001-oem.Jpg
and have plugs like this
https://images.duckduckgo.com/iu/?u=https%3A%2F%2Ftse1.mm.bing.net%2Fth%3Fid%3DOIP.M32895bf6dec0eb04266c2efd4ef4bb84o0%26pid%3D15.1&f=1
if so I think the gt 730 is the best bet.