are the diffs interchangeable? right now i have a regular sr5 diff with sr5 rear end. could i (for now until funds allow), use the gts lsd diff with the sr5 rear axles? i have a gts driveshaft. thanks.

no, theyre a smaller diameter, youll need a full gts rear. FYI, zenki and kouki axles are different diameters as well. the lengths from open to lsd are different too, I believe you can shorten an open axle to fit the lsd, but I would recommend searching for that length info, im not 100% on the which to cut, or how much, in terms of the length

From past experience I remember shaving roughly 5mm off the ends of Non-LSD axles to fit the Stock or TRD differentials. I know for sure Kazz & cusco rs/mz accept both open and lsd axles, haven't tried any other brands though.