Back in that era the Yaesu FT101E has a square wave inverter built in for DC ops using a standard transformer and did fine due to the flywheel effect of the transformers core and the filter caps. A modified sine wave inverter should be better, I'd do like syfr says and try it out. IF you get hummmmm i'd replace the old drying out electrolytic filter caps. Otherwise you should be fine.
Just have plenty of battery capacity, 400 watts at 13.6v is ~30a peak draw.
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