Simple job really. Condo built in 1980. Kitchen cabinets L shape, a 6' fluorescent 2 bulb on the short leg, 8' fluorescent fixture on the long leg, not working, and I don't want that long thing up there anyway. These are laying bulbs up, on top of the cabinets.

A concrete ceiling, so I just as soon replace the long one with a 4' T8 fluorescent fixture, I don't want LED. So googling around I found an outfit called 'American Fluorescent, assembled in USA. I had gone to home depot and the lithonia made in Mexico fixture got poor reviews on amazon.

The installation instructions say that buildings before 1985 have wire rated at 60C, and this fixture needs feed wire rated at 90C. So how do I know what I have ? How much does it matter ?

I've wired outlets, ceiling fans, odds and ends. So I'm not clueless about it, and feel competent to do a simple thing like this. Any info would be appreciated.