Just fair warning... you may have trouble finding a used t5 from a v8 car that isn't trashed. And not all v8 t5's are the same as far as strength is concerned. Your best bet is to get a t5 from a 94-04 v6 mustang. They have a slightly longer input shaft, which sets your shifter back about 5/8". That's a good thing, from what I've found. The fox length input shaft and bell put the shifter too far forward. Not an issue with factory shifter but causes clearance issues on most aftermarket shifters with adjustable stops. Locating the shifter back slightly also makes it easier to reach your front two shifter base bolts.
I want to say 86-89 gt t5's are rated at 265 ft-lb. 90-95 v8 t5 rated at 300. 94-98 v6 rated at 265. 99-04 v6 rated at 300. You have about a 99% better chance of finding a good t5 from a v6 car and they are usually much cheaper because most people don't understand they can be used in v8 cars fairly easily. The 94-98 v6 t5 can be bolted right in with a 94-95 v8 bell. You can also swap in a shorter fox v8 input shaft and use a fox v8 bell...OR you can buy a spacer that allows you to use the longer input shaft with a shorter fox bell.
The 99-04 v6 t5 is stronger, but the tailshaft housing is set up for electronic speedometer. You can swap a tailshaft housing from an older style (has to be world class but can be 4-6-8 cylinder version). You'll have to drill a small hole in the main shaft to swap in a speedo drive gear and retainer clip to work with a mechanical speedo. The shaft is hardened steel and not easily drilled, but a diamond bit on a dremel does great.
While the tailshaft housing is off, you can add a billet steel cluster support plate for under $50. Easy upgrade that helps add strength. Another mod is to buy shim kits for both the input shaft retainer (to set end lash on the main shaft) and the cluster/ counter shaft. Shim both shafts to where there is a very slight preload. They're set up a little loose from factory.