"...wheras (I believe) the originals were an alloy of copper and nickle (the same alloy that a U.S. 5 cent piece is made out of)."

Tom,

I suggest a magnet test on your OE hard lines. I have a bunch of 140 lines that are definitely steel. To the best of my knowledge, the copper alloy lines began with the 240 (see quotes below -- sources forgotten). I doubt that Volvo would go from a copper alloy on 120, to steel on 140, then back to copper, but who knows? A magnet will tell you real quick.

I also doubt that those new replacements are plain copper, since the cupro-nickel has been around since the 70's.

Copper Alloy Brake Lines:
"...Efforts to achieve a metallurgical solution to the corrosion problem continued. Volvo began the use of 90-10 copper-nickel ("Cunifer Alloy") tube in their 1976 model vehicles and have been using it since. Figure 1 shows the installation at the master cylinder in a 1990 model Volvo. Audi began using this material in 1990. The other European cars using this material are Porsche and Aston Martin."

"Users of copper-nickel brake tubing in addition to Volvo include world-class vehicle manufacturers like Rolls Royce, Lotus, Aston Martin, Porsche and, most recently, Audi. Copper-nickel is also used in military, fire fighting and other heavy vehicles."
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.