I am doing a similar build w/700c wheels on a lovely old Trek 990. ( Made in USA! )
Would think the ability to do this varies from MTB frame to frame depending on the frames' structure: where the brake bridge is etc.
Some MTB frames work better than others.
They make some rather long-reach calipers, so you might have to dig in some parts bins until you find one which works.
For the front you can use a 700c cyclo-cross or gravel type fork and have more possibilities.

and yeah keep in mind: Certain tire manufacturers make super fast , narrow and streetable 26 tires...