Engine Suggestions

Ok... I asked this last year one other time. I am still not too sure on working this thing. I have a 97 Powder Extreme that has no engine, CDI, coil, carbs, clutches, and all I have are the stock pipes and can. Sled is in excellent condition otherwise and very worth saving. My question ultimately is... What engine should I go with? I ride up in the Mountains of CO and WY so I would like to keep weight down for powder running but keep trq and speed as well. I have a 95 EXT powder special 580 that I will have for a sled until this one is running... But I was thinking more along the lines of a larger twin with carbs. Fabbing it in there shouldn't be too hard with the stock mounts for the same chassis sled and similar size motor. I am thinking more along the lines of price than I am HUGE HP... I was going to use my other sled as a bargain chip, but with engine size, chassis, and age of it I think it would be worth more to me... That and I like to have a back up sled if you know what I mean... So I am open to suggestions. Anyone here got any???

Thanks cat fans!!!