No, but it will get better fuel mileage if you do.
There really isn't an adapter plate, but look into the T-4 bellhousing for the 2.8L Mustangs.
The 2.8L, 2.9L, 4.0L OHV share the same bellhousing pattern, and apparently the 2.8L T-4 bellhousing can be adapted to the T-5. I am very uncertain of the swap, as I've never done it before. I had planned to, but scrapped my 2.9L plans for a V8 swap.
I have a 10,000 RPM aluminum flywheel for 4.0L/2.9L T-5 conversion that I am probably going to want to be getting rid of soon due to V8 swap. The throw out, clutches and pressure plate are all shot, but at least they're there and would be shipped w/ the flywheel. PM me if you are interested.
Pete