I can't comment on using a double flare tool to make a reverse flare. I will comment that if you buy a tool, do not go for the cheapest that you can find. There is a local discount tool store in Canada that had some inexpensive flare tools for sale and they were all slightly out of spec - net effect the fittings all wept fluid.

If you are fabricating new lines, use the nickel-copper lines that Eric mentioned. Its a little more expensive; but, it is so much easier to bend and form than the basic steel lines.

I would skip the generic auto parts places like NAPA. Chances are that a good brake shop may have the flare fittings you need and can fabricate the required lines. I replaced most of the lines on my 142 when I rebuilt it and had a local hydraulic hose specialist fabricate my hard lines for me. He also fabricated stainless steel flex lines for both front disks and the two axle lines for about $50 more than the cost of new rubber lines plus shipping.

A word of advice on bleeding the system. Use the procedure set out in the Volvo service manual - much easier to get the air out of the system. If you are using the pump the pedal style of bleeding, do not press the pedal to the floor if you have an old master cylinder. The master cylinder walls wear with use and develop a slight ridge at the end of the normal piston travel. If you force the piston past that ridge you risk damaging the seals on the piston and the MC will develop a condition where fluid is leaking past the piston resulting in the pedal gradually sinking to the floor when you apply the brakes. Much better to use a pressure bleed system, particularly with all the bleed ports on the 140 series.