Finaly got my junk together and swapped my stuff out.
figured I'ld post some results....
Patient: '91 Chevy Sprint hatch
Donor '96 Pontiac Firefly 4-door brakes
swapped the whole knuckle assembles, 4 corners & bled ~ 5 un-hustled hours
Everything bolted up GREAT, even the banjo bolts. Only mis-mash was the axle seal. For some reason it was a Geo Metro seal, the 'Sprint' one had a smaller I.D. Which doesnt make sense, because it didnt even match the ones that were originally IN my Sprint :-S
The rear was just as easy, minor bend of the brake line and it screwed right into the wheel cylinder.
E-brake cables are a little long, but I didnt check if the drum sides are the same, might be able to re-use the shorter lines (I was in a hurry, and swapped it as an assembly). Even the brake master cylinders have the same bore.
Cons:
lil hunting, lil time
Need new wheel nuts
Need larger tire/wheel combo
Pros:
Larger rotors(5/8") AND vented
Larger drums (11% diameter / 75% width)
Bigger bearings
Bigger spindles
Rotors slide over top of the hub
Drums slide over top of the hub
12mm lug studs
Need larger tire/wheel combo

As for alignment, it was uber close, just needed a toe adjust. Had the mis-alignment pinch bolts just incase.
Havent jumped on the brakes yet, letting them bed in a lil longer first, but the peddle feels alot more firm, could be from bleeding out the brown brake fluid too tho.