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MWTo date, all examples I have seen exhibit an after-factory cut and do not appear to have been inserted in wax packs. That being said, many (a couple dozen) examples have been graded by PSA and probably a few have been encapsulated by other companies as well. I believe the reason for this is because some gray backs have a much straighter cut than others (i.e., they have qualities that closely approximate "regular" 1948s).
The values for these cards is somewhat arbitrary. Ungraded, you're probably looking at a range of 75% to 125% of what the standard 1948 Bowmans sell for. Graded and with a uniform appearance (straight cut), you might see a slightly larger premium.