Same old, same old
Better to replace with new than try and port very old no matter how well it works. Things have moved on in the last 50 years.
When I worked at EDS the porting projects invariably failed, the replace with new and migrate the data were normally were successful.
But they did make the classic EDS outsourced mistake on one project. Letting go the coders who were keeping the old system going by patching the code. PL/I can be an unforgiving mistress. They had to rehire 2 of them at great cost as contractors. Nice guys, but one looked like a 1960's OU lecturer and the other a badly aged member of a 1970's glam rock group, who still thought flares were cool.