I would personally get a modern Shimano Deore LX long cage RD, a wide range cassette (11-34?), a longer chain and ride away!

I obviously don't stress keeping my bikes period correct.

The gap between gears could be pretty large in cases, but unless you combine the above with a triple, you aren't going to get much lower gearing.

Compact (110 mm BCD) on the front with something like my favorite chainrings (48-34) would be good if you want to keep a tighter geared cassette.