Richard,
Your 5-speed T9 is a great trans but will require a few things such as shortened drive shaft, (probably) different speedo drive (wheel size, etc, you'll be tooling at 100MPH on the speedo and 70 actual!) and you should review and likely change 1st gear while you go over the trans because the weight of the Merkur is so different that you'll be changing to second gear before you cross the intersection from a stop.
Dave