I've, for many years and on four 240's I've recently had, used Eurosport Tuning & Brakes's slotted brake rotors, and IPD Deluxe pads, to enhance my cars' braking (along with better shocks, IPD antisway bars and tower-to-firewall braces, etc.) -- I enjoy enhancing my cars' performance. But on a current project, putting together a 1993 car (with ABS, of course) to give to my daughter, I've -- with trepidation -- taken a new (for me), further step by installing IPD's braided stainless brake lines.

I was nervous primarily because of the "horror stories" I've read here in the forum -- paraphrasing a typical example as, "I couldn't get the fasteners loose (even with a torch), and I messed up and had to replace the metal lines, too!" It sounded like this sort of thing happened too often for my reassurance and comfort!

So I took everyone's advice (and a big Thank You to this forum!):
1) Got a pair of Snap-On-brand wrenches, 11 and 14 mm (RXSM11B and RXSM14B), each with a regular crescent on one end and a flare-nut on the other (but more comments about these further below);
2) Generously applied PB-Blaster for a whole day and evening, repeating almost every hour (alternating with Brake-Kleen to flush the crud away).

Okay, granted, this 1993 isn't as old as a '80's or late '70's car, but it had 130,000 miles of New Jersey roads (including winters with salt, etc.), and yet I have to tell you all that it worked like a charm!
All I did was apply just some moderate pressure to the wrenches with just one hand (using the grip method), not even like a stuck bolt, and they just "gave" -- the fasteners separated like a dream! Putting the IPD braided stainless lines on (only one on each side -- it has ABS) took maybe five minutes on one side (lots of threads to turn), and about 10 minutes on the other (had a little trouble threading it on the strut end because of the angle).

But, some observations regarding the Snap-On wrenches for those of you following in my footsteps:
1) The SnapOn brand wrenches are truly a more precise fit! No wobble at all, compared to my regular wrenches (Craftsman, Action, etc.) -- well worth their high price!
2) The end nuts on the IPD lines aren't exactly the same size as the OEM lines' end nuts! Yes, they're still 14mm, nominally the same as the OEMs, but a little bigger nevertheless (definitely not for a 15mm wrench). The Snap-On 14mm wrench, which fit the OEM lines' nuts perfectly, could not be fitted on these new IPD lines' nuts! Yes, the 14mm Snap-On wrench is so precise that any nut that isn't as precisely sized is too big! So I had to use my other brand wrenches (both Craftsman and Action fit) to tighten these new lines!
Of course, if you're just putting on new OEM flexible lines, then you can use the Snap-On's to tighten, too!

Well, we all know the danger of using a wrench that isn't a precise fit (rounded nuts), so if anyone ever doubted whether the Snap-On wrenches are worth it, I can tell you that there IS a difference!

So, in summary: use only Snap-On wrenches to loosen, and use plenty of PB Blaster beforehand! At least in my case, no torches, no rounded nuts, no trouble at all.
Thanks, Brickboard, for the advice!!!
Best regards, all!