Some OKI's require a change in the Parallel Port configuration for the JetDirect. I'd first move the OKI from Port 3 to Port 1(or 2) to see if the problem follows the printer, or is back on the SCO configuration. Also, you shouldn't have the ":ex" parameter set in /etc/printcap. Please provide "the rest of the instruction" from your printcap lines. What you provided doesn't show all the required settings.
Given a choice, I'd opt for using HPNP instead of LPR/LPD. You have to do some manual tweaks in the interface file to send to ports 2 and 3, though.
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