I've been thinking about putting an aftermarket TBI on my 83 blazer, something like a commander 950 from Holley. I notice that my mechanical fuel pump is the kind with a vapor return line on it already, so there are two lines going to/from the gas tank. Is there any reason why I couldn't use this line as the return for the fuel injection system? If I could, it'd make the install a million times easier. Is there an obvious way to tell which line is "from" and which is "to" the gas tank?