No need to go 29'er. A 26" rigid fork will probably have enough clearance for a road wheel+tire, and the axle-crown length will be much closer to that of a road fork. The Kona project 2 fork is VERY popular, and I think they even have a CX version specifically for this purpose.

Also, Surly forks are ass-heavy. Don't look to them for saving weight. Here are some other options:

Carbon CX fork with disc mounts

The Kona P2

Dimension disc CX fork

Even the cheapest is less than a Surly fork, and weighs less than 1.5 lbs.