Can this old portable CRT TV connect to a RPi?
You'll want an old-school RF modulator: https://en.wikipedia.org/wiki/RF_modulator. These were common in the days prior to baseband composite inputs on TVs. They basically are an upconverter-in-a-box: they take the composite signal and upconvert it to the VHF broadcast band so that it looks like an over-the-air signal to the TV. You simply tune to the channel the modulator upconverts to, and presto, you've got video.

If the TV doesn't have a coaxial input for the antenna (ie: it has integrated rabbit ears), you'll need wire one in place of the antenna. In this case, you may also need an attenuator between the modulator and the antenna input, as the RF frontend of the TV might saturate above a certain input level. I would try without an attenuator first, though.