Daz,

There is more to it bud, welding is needed as you need to add some lugs as the mountings are wider on the Tremec than what the T5 bellhousing is
You also need a spacer plate too between the gearbox and bellhousing.
Also you have to run a smaller bearing in the crank as the input is larger.

Not the best pic but best I have on my computer, here you can see the added on tabs for the fitting on this side