I'm working on a similar FI mod. on my 67 122. I'm converting to K-Lambda on mine.

What I have done is drill and tap (and sealed with extra JB weld... thin tank material) a second fuel line close to the original one except lower. Then I used the original line as the return. On the new line, I used what is called a thermocouple fitting that allows a section of 3/8" stainless tubing to be inserted thru the fitting and in to the lowest point in the tank (which is the close to the same as the Volvo did with the original line). I used this method because I didn't want fuel supply problems caused by a low fuel level in the tank (note 240 pre-pump failures) thus keeping the inlet to the fuel pump low in the tank should eliminate any fuel feed problems and I also wanted a larger fuel line to the fuel pump. I am using a pump assy out of a K-jet 240. I then ran new plastic line, the same as new cars, to the FI filter in the engine compartment.

I haven't yet started the car. I'm running a new exhaust at the same time and the weather hasn't co-operated to get under it. But it is the same method that worked perfect on my old VW rabbit that I converted from diesel to FI.

I thought of installing the return through the top, but didn't want and additional lines and fittings sticking up in the trunk.

Good luck