10.20 is ancient in HP-UX terms.
Default tool for printing in HP-UX is JetAdmin (later rebranded as HPNP). This didn't use "drivers" so much as "models". If you got a "model" for HP-UX 11.x chances are you can make it available in your HP-UX 10.20 system.
I haven't really done any HP-UX to Linux printing mainly because I'm using JetAdmin/HPNP on all but one environment which IS running 10.20 but there we use CEPS rather than CUPS.
Not a lot of support here for HP-UX. You might want to post on itrc.hp.com or on the Dutchworks mailing list.
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