I'm not sure if this would be an option, but if a whole bow is out of the question, are there people out there who could custom make 80# limbs for your Samick riser? I'd guess limbs would be a little less expensive than a whole bow, but then again I've never looked into it myself.
As a side note, while I'm always up for experimenting with things, would you regret it if your modified Samick limbs failed before/during your hunt in Africa (and looking back and saying "Man, I should have spent the $$ on the 80# bow")? If you'd have no regrets, then I wish you the best of luck.