Boost it with a home built kit as it sits, don't change anything, just boost it. It will be a great learning experience for you on an engine that you won't worry too mcuh about if you blow it to smithereens. If you do blow it up, you can replace it cheap and be driving right away.
Then start saving money for the B swap. Plan it all out to be boosted from the very beginning. Use what you learned on the D, to plan out an excellent path on the B. Build the B on an engine stand, and even mock up your turbo stuff. The more you plan / prepare, the easier the final project will be.
When you are ready, do your swap.
When the swap is done, sell off the old boosted D to a friend, with all the old boost gear with it. Use the money to start on your next project a boosted, stroked, GSR, overbored and built to the hilt. Or a race car, or...
You can easilly reach 200with the little D motor.
Craig