Hey, Rick's semi-insulting response was actually almost on-target.
Lia, a front trike, or "tadpole" trike conversion would be horribly complicated. Even if you managed to acquire the whole front end off of something that used car-style Ackerman steering (where the wheels turn at slightly different angles to avoid drag during sharp turns), your center of gravity would make it difficult to actually make any of those sharp turns.
Production tadpole trikes either lean (like the Piaggio MP3), or are very wide and low (like the CanAm Spyder).
It would look awesome, though.
Still, you can probably make your Batavus into a "normal" trike using a bolt on kit. They made these for Puch mopeds (Called Tri-Rads I believe), and for a couple of other kinds.
The big obstacle here is acquisition; if you can find one online (ebay had a trike kit a while back, as did the Buy/Sell forum), you can probably find either a motorcycle shop or a friendly soul in your area to install it for you.