The steel frame will likely take the punishment okay.
From what I remember of that bike (yeah, I'm old), they had steel rims? But that's not really the issue as far as making the bike (and you) better suited to the rough commute.

First thing to consider is the tires. It's probably the most cost efficient improvement you can make. Look for something like 1.25/32C width with flat protection.

Second is to give you butt a break. In Europe, where many people use bikes for basic transportation on rough roads, sprung saddles are commonplace. Another option is a Thudbuster seatpost.

Third is to give your hands a break with padded handlebar tape and/or gel gloves.

Unless you're thinking of trying to preserve the bike for historical reasons, the changes will be inexpensive enough to help you get by for commuting. If you're thinking about spending more than $100 or so to make it more comfortable, you might be better served with a used 10 year old mountain bike.
Potato/potahto.

Enjoy the commute!