It's not a matter of spending money, it's a matter of wasting it. The only reason to use a B20 block, is so it says "B20", otherwise, it's better to resleeve you stock block, you'll get as much if not more power, and since you're sleeves will be thicker, it'll also be basically bullet proof. Plus it saves you the expense of puting all sort sof extra parts just for it to work right.

In the case of not having a motor, and just having a B20 sitting around, that's about the only good reason I could think of for starting that kind of a project.

In any case, good luck.....