Don't build it.....
Phoenix Contact makes a small DIN rail mounted module that will convert just about any millvolt and/or amp signal to any other millivolt and/or milliamp signal.
Check out this link:
http://eshop.phoenixcontact.com/phoenix/logon.do?user=anonym&general=enen And search for part 2810913 MCR-C-UI-UI-DCI
Using DIP switches it can be set up to change just about any signal into any other signal. It's very nice. No idea of cost but I was about to buy one to solve a problem that I have. I think they run a couple hundred bucks....
I think they also make a unit that can be programmed for unique input and output performance.
RSlater,
RSmike