Help on 85 REX

I have an 85 carbed CRX that i'm gonna drop a DOHC ZC motor into :). The obvious problem being that it has a carburated fuel pump. Can anyone please tell me if the sending unit on the carbed and the sending unit on the Si are interchangable or do i need to replace the entire fuel tank with that of an Si. It seems like if i were Honda it would have been cheaper to manufacture one tank and just have different sending units (at least that's my hope). Any help will be appreciated. Thanks in advance.

Kris