Mike - Great find. For collector value, it would be wise to take the advise of Bjorn and John, and leave the bow as is.
In the 1958 Kodiak sow belly bows, the 56" length is far and away the rarest.
There are a few variations within this length and year of the sow belly Kodiak...
1) 56" no accent stripes (rarest variation)
2) 56" accent stripes with scalloped sight window corner
3) 56" accent stripes with rounded sight window corner
These variations can also be found with or without factory camo. I don't really collect factory camo Kodiaks, but have a few that are original factory camo or originally were factory camo.
Judging from the serial number, (Kodiak serial numbers are not always 100% accurate), I would guess that your 56" Kodiak is the last variation (3) listed.
Occasionally a heavy weigh 56" Kodiak will surface, but they are uncommon. The heaviest 56" 1958 Sow Belly that I have is marked 60#@28". I have never scaled it at 26", but is is likely a pound or two lighter than your 57#@26".
As far as rarity of 56" 1958 compared to the 56" 1959, I'm not aware of an actual inventory of 1958s that has ever been taken.
Of course, the 56" 1959 has received far more notoriety and is generally considered by most serious and novice Bear collectors to be far more eye catching.