I've read up on the site what folks recommend and I went and bought some very good steel lines from Advance. The lines have a nice coating on the outside, bit like the OEM lines. Right, so I bought 1/4 for the return line, as recommended. But it seems a bit small. I have the broken bits of the OE return line and it fits sungly into the rubber line; the new 1/4 steel line does not, bit loose. Does it matter for the return? And not sure if this means I should go up in steel line size or down in rubber line size. Thanks for any advice.

Most FI systems I've seen have at least the same size or larger line on the return side.
FI pumps move a high volume of fuel so the return line needs to be large enough that the regulator can maintain the right pressure for the injectors by bleeding off all the excess fuel. If the return is not large enough its likely the system will over pressure and the pump will burn out more quickly.

Maybe return should be 5/16 (8mm)?
-G

You'll want your return line to be bigger than your feed, so that the fpr can do its job properly.

Helpful, thanks all.

Got the new line material, cut it, flared it, got it roughly installed. Was easier than I'd thought...but I'm not quite done bending.

Wondering about pointers for how others have run the line. Does it get held inside by the bendy metal tabs? Okay if the lines touch each other, attached to each other with zip ties? Need I worry about having them pinned down tightly or does it matter if they are just above the floorboard?

you have to remember the original sizes were metric so the metric equivalent of 1/4" is probably just a bit bigger