Perhaps the better question we should be asking is what is your budget for this 5 speed swap? The Merkur T-9 is likely a very hard find and from what I've heard not as stout as a T-5. The Quaife T-9 that Pintosopher mentioned is likely $3,000+ to your front door. A self pulled, 2.3*, T-5 (if you can find one) from a self serve wrecking yard is likely about $150. That is quite a cost difference.
*You mentioned " Found PLENTY of World Class T-5s on E-Bay." BE AWARE I just did an Ebay search of "T-5 Transmission" and of the first 200 hits that came up NONE were for the 2.3 Ford version of the T-5. They were either the Mustang or the Camaro. The Mustang trans has a different length input shaft and the Camaro like wise, plus in most years the Camaro had a different bolt pattern. S-10 T-5's are also different. I then did a search for "T-5 Transmission 2.3" and ONE transmission came up. I see 2.3 input shafts on Ebay in the $80-$100 range but I'm not sure that is all you need to convert the 5.0 trans. Plus for better or worse you get the 5.0 ratios.
I live in So. Cal. where cars linger longer and parts tend to be more readily available. I went to two self serve yards nearly every month for the past 20 years. I'm going to say in the past 8 years I've seen two T-5 Turbo Coupes and maybe one to none T-5 2.3 Mustangs. So, even 2.3 T-5's aren't just lying around on the ground. Think this through before committing. Tire size, rear axle ratio, type of driving, budget, mechanical skills, expectations, alterations (driveshaft, speedometer, shift lever location, clutch disc etc.) - are just a few things that come to mind.
I was fortunate that my '88 Turbo Coupe was my daily driver for 10 years. An insurance pay out (other parties fault) basically made the car free. It just so happened that my C-4, 6-3/4" rear end driveshaft fit perfectly to my T-5, 8" swapped rear end without alteration. I still had to hunt up a 86 or older bellcrank bellhousing (87-88 were hydraulic), pedals, cable, make the trans crossmember modifications, create a new cable mount (elevate over the crossmember), shorten the shifter etc.. So it is not just out with the old and bolt in the new. I'm not trying to discourage, but I do feel a responsibility to present many of the aspects of the swap.
Update: I ran the tag number and it is an 87-88 Mustang/Capri 2.3 trans. So, it is WC. 1352-162 Ford 87-88 Mustang/Cap ri 2.3 240 3.97 2.34 1.46 1 0.79 3.7 7T Y(WC)
http://www.mongosgarage.com/tech/t5/T5Numbers.PDFHere is the Ebay link:
Pa&vxp=mtr" class="bbc_link" target="_blank">http://www.ebay.com/itm/Mustang-t5-transmission-87-88-2-3-79-93-ford-/122625095872?hash=item1c8d0678c0:g:iHMAAOSwj85Zf0 Pa&vxp=mtr