Since you are only changing the mechanics of the core rule set and Hyboria's Fiercest deals with mostly regional variations to Barbarian, Border, and Nomads I would think you could utilize the information regardless of the system you are using. The multiclass section would be very helpful in diversifying the types of Fierce characters you could play.
The new feats could be worked into your different system just like feats presented in the core book.
the book contains alot of great information but not sure which other systems it can be used on.the sub groups are very conan but those races are for conan unless you nick the entire world dont know.the scholars spells and items are again very conan and the mix and match classes are very conan but how many other games allow barbarian/pirate/noble mixes(ie conan himself)it is one of the key strengths of the conan system but it is not like some other publishers just a list of feats their is some meat here but vey conan flavoured meat hope that helps 8)
I'm not really interested in feats or classes. I'm using Rolemaster as a system, so that kind of stuff is irrelavant. What I'm wondering is how much non system material (ie Hyborian info) it contains that I can integrate into my campaign.
I think you guys have given enough to go on though. Thanks for your help!
There are definitely supplements and books available to add to the atmosphere and setting in the Conan RPG besides Hyboria's Fiercest (which really just expands the three classes of Barbarian, Nomad & Borderer's) like Road of Kings, The Free Companies, The Aquilonia HC, The Book of Skelos & the original Conan stories available unedited by Del Rey: The Coming of Conan and The Bloody Crown of Conan!