speedometer hookup help

[stan79chevy]

as some of you know im in the middle of a rebuild on my 79 we did the motor last summer and the extra power killed the tranny, transfer case, and the rear end.. since then i have gotten the th350 completely rebuilt, replaced the half ton axles with 3/4 ton stuff. and i got a 205 transfer case instead of the 203. i have the axles in and they have 4.56 gears. my question is my speedometer is going to be way off because i originally had 3.08 gears. i still have the 205 that came out of the truck that i got the axles from. can i take that input thing off that one and put it on my other 205? is that where the "gearing " thing for the speedo is? or is teh gearing thing in the speedometer itself? my truck is a 79.. the axles are 77 and the transfer case is a 70. thanks

stan