Whether or not you'll need (slight, easy) modifications depends on whether your '79 has the 12V
fuses as an integral part of the Univolt, or in a separate panel.
If they're separate, and you don't mind dealing with old-school glass fuses, it should be a pretty easy swap. A new 45- or 60-amp converter will probably just have a 120V plug and the +/- 12V
outputs, with integral fuses. If you don't have a separate fuse block, you'll need to install one, and move the 12v
supply lines for each circuit from the univolt to the new block. I *THINK* by '79 they had a fuse block that was independent of the converter. Making your gauge in the control panel work with a new converter is another matter, but since I have no central control panel I haven't studied that.