This is what I know about Holset turbos's, and I use to be into 2.3liter turbos on Ford motors. The wast gates are the opposite of T-3, so if T3's are external wastegates the Holsets are internal. Also, the flang that connects it to the exhaust manifold is diff. but there is a company that sells a adapter for it. You can search it on the http://www.turboford.org site. Also, they have alot of diff. compression wheels, so you can mix and match to your taste. Also where the turbo connects to the downpipe is alot diff. than a T3 but nothing a muffler shop cant fix. Also parts a rear, and more expensive, but they do have a direct website with flow numbers on the site in .pdf files you can download, and print. I'll try to get the site for you.
Now for the GREAT news!!! They are the most efficent turbos out there!! They spool quicker, and have more top end push than almost all other turbos period! All the test that where run on Fords where flat out scary!!! I have found the most info on these turbos at http://www.turboford.org than any other site.
That's all I know about them.