Evolution is a 1 1/4" steerer tube, so you'd need some head tube shims and a new threadless headset as well as a 1 1/8" fork with disc mounts. Add a threadless stem in the mix as well. If you wanted to keep the original front brake lever, you will need a BB7 road disc caliper, as well as a new front wheel.

All of this could easily cost you over $300 in parts alone even if you shop around for deals.