i say get a GTS! by the time you do all the conversion on it, you gonna waste so much money,
the suspension on SR5 and GTS is different, and most likey when you're gonna do a suspension upgrade, you gonna probably install the GTS suspension....
if this car is not your daily driver, what you can do is purchase another GTS and swap all the parts on to the better condition SR5 body... but also heard that GTS body is lot more firm then SR5 cuz its been reinforced with spot welding...
Tis not Cheap Hobby