Are these steel rims safe?
Some old wheels do not have a hook to hold the tire bead, which limits you to around 70 PSI. Straight wall or a slight flare, doesn't matter, 100 PSI is not doable without the hook, afaik. (Wikipedia says the hooks were invented in the 70s)

In my experience, the tire will come off within an hour or two, and the tire will pop off with a bang as the tube explodes. With straight walled rims, I think 700x23 tires are unusable. There may be some uncommon rim design that I'm not familiar with, but if your rim wall looks more or less flat, it's not going to work.

And the fact that they are steel makes blowout more likely if anything, because they are more likely the old design.

If they have a hook on the rim, I would ride them after I let it stand for a day, but steel wheels really do suck for braking.