I haven't worked on a bike since the 70s, but recently started fixing up an old road bike from the mid-80s. My question is- Are the cable ends on modern bikes the same as the old tension shifter and non-aero bike cables? I don't want to buy a cable that won't fit into the brake lever or shifter

Brake cable cables come in two different styles. One has a mushroom shaped end the other has a barrel shaped end. Some generic cable sets have one of each and you cut off the one that you don't need. A mid 80s road bike might need either.

Shifter cables come in two styles too. There's Campy and there's everything else. The Campy ends are just a skosh smaller.

Plan on having to cut off the extra length. I use a cable specific cutter for that job because the end doesn't fray as badly. I prefer to buy my cables over the internet and buy "slick galvanized" cables. Slick cables are drawn through a die so they're smoother and galvanized steel cables are easily soldered. I solder where I plan to cut the cable and cut through the solder. If you do a neat solder job it will never fray and can even be drawn back through the cable housing and replaced.

To add,

Most drop bar levers take the mushroom type brake cable, and most upright bar levers take the barrel end, which slides into the lever sideways then rotates forward to be locked in place.

Gear wires are now as described above, with Campy heads being slightly (imperceptibly unless measured) larger than the common "standard". However there were other heads used in the past, so if your gear levers appear to be modern types you're safe to assume they're the same as current. But it's not a given, so look at the lever before buying.

Housing and cables are better now than they were in the 70s .

thanks for the info