When I researched kits for my 56 (sorry, not the same as your 58) I found considerable variation depending on the manufacturer - all of them moved the wheels out some:
CPP - 3/8" per side but with 2" dropped spindles only 1/8" per side
Summit - 1/4" per side
ECI - 1-3/16" per side (huge!)
Speedway - 7/8" per side but with 2" dropped spindles only 5/8" per side
Heidt's 2" dropped spindles - 3/8" per side
IMHO under 1/2" per side will not cause tire rub on fender and slightly increased track will make the car look better.
Hope this helps.
Dave
__________________
1956 Pontiac Pathfinder 2dr sedan, 496 - dyno'd 545 hp, stick shift, 4.11 posi - Hot Rod
1956 Pontiac Pathfinder 2dr sedan, 496 - dyno'd 545 hp, stick shift, 4.11 posi - Hot Rod