Ive been considering converting a big mtb frame with a front shock into a touring rig, but it seems that replacing the fork would change the angles in a bad way.

Do any of you gurus have a recommendation on how to get around this?

Look for forks with "Suspension corrected leg length meaning your bike's handling won't change" Measure the current axle to crown measurement and try to buy a fork with similar dimension of length.

How much travel does the current fork have? If it is just an 80mm, don't worry about it, the Surly 1x1 fork will be fine.