will the gears from a 84 dodge w200 3/4 ton fit in my 99 ram 1/2 ton ? both are dana 44, but someone told me it wont work the same way since they are not both half ton....?

You would have to check the BOM numbers on the axles. My guess is that it won't, but that's just a guess. The fact that you're comparing 3/4 to 1/2 ton is probably not the best or even a viable way to compare the two axle parts' compatability.

If you search the two trucks front axle parts on Summit racing's site some of the part numbers seem to cross over such as Superior axle and gear's open differential carrier, but I'm not sure I would take that as a 100% sure. Again, get the BOM numbers off the axles, or just try it and see if anything interferes with just a mock up.